Chapter II: Part I: Amphibia (1)

"'s scheint, dass die hier oben keine
Ahnung haben von dem Sumpf und
Seiner Pracht."
The "plattgedrückte Kröte,"
SCHEFFEL'S _Trompeter von Säkkingen_.

{3}CHAPTER I

AMPHIBIA

CHARACTERS AND DEFINITION–POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA–HISTORICAL ACCOUNT OF THE CLASSIFICATION OF AMPHIBIA

A bird is known by its feathers, a Beast by its hairs, a Fish by its fins, but there is no such obvious feature which characterises the Amphibia and the Reptiles. In fact, they are neither fish, flesh, nor fowl. This ill-defined position is indicated by the want of vernacular names for these two classes, a deficiency which applies not only to the English language. All the creatures in question are backboned, creeping animals. Those which are covered with horny scales, and which from their birth breathe by lungs only, as Crocodiles, Tortoises, Lizards, and Snakes, are the Reptiles. The rest, for instance, Newts or Efts, Frogs and Toads, are the Amphibia. Their skin is mostly smooth and clammy and devoid of scales; the young are different from the adult in so far as they breathe by gills and live in the water, before they are transformed into entirely lung-breathing, terrestrial creatures. But there are many exceptions. _Proteus_ and _Siren_ the mud-eel, always retain their gills; while not a few frogs undergo their metamorphosis within the egg, and never breathe by gills. If we add the tropical limbless, burrowing Coecilians, and last, not least, the Labyrinthodonts and other fossil forms, the proper definition of the class Amphibia,–in other words, the reasons for grouping them together into one class, separated from the other backboned animals,–requires the examination of many other characters.

{4}So far as numbers of living species are concerned, the Amphibia are the least numerous of the Vertebrata. There are about 40 limbless, burrowing APODA; 100 URODELA or tailed two- or four-footed newts, and about 900 ANURA, or tailless, four-footed frogs and toads; in all some 1000 different species. Few, indeed, in comparison with the 2700 Mammals, 3500 Reptiles, nearly 8000 Fishes, and almost 10,000 Birds. But we shall see that the Amphibia have not only "had their day," having flourished in bygone ages when they divided the world, so far as Vertebrata were concerned, between themselves and the Fishes, but that they never attained a dominant position. Intermediate between the aquatic Fishes and the gradually rising terrestrial Reptiles they had to fight, so to speak, with a double front during the struggle of evolution, until by now most of them have become extinct. The rest persist literally in nooks and corners of the teeming world, and only the Frogs and Toads, the more recent branch of the Amphibian tree, have spread over the whole globe, exhibiting almost endless variations of the same narrow, much specialised plan. The greatest charm of the Anura lies in their marvellous adaptation to prevailing circumstances; and the nursing habits of some kinds read almost like fairy-tales.

CHARACTERS OF THE AMPHIBIA.[1]

1. The vertebrae are (_a_) acentrous, (_b_) pseudocentrous, or (_c_)
notocentrous.

2. The skull articulates with the atlas by two condyles which are formed
by the lateral occipitals. For exceptions see p. 78.

3. There is an auditory columellar apparatus, fitting into the fenestra
ovalis.

4. The limbs are of the tetrapodous, pentadactyle type.

5. The red blood-corpuscles are nucleated, biconvex, and oval.

6. The heart is (_a_) divided into two atria and one ventricle, and (_b_)
it has a conus provided with valves.

7. The aortic arches are strictly symmetrical.

8. Gills are present at least during some early stages of development.

9. The kidneys are provided with persistent nephrostomes.

10. Lateral sense-organs are present at least during the larval stage.

11. The vagus is the last cranial nerve.

12. The median fins, where present, are not supported by spinal skeletal
rays.

13. Sternal ribs and a costal or true sternum are absent.

14. There is no paired or unpaired medio-ventral, copulatory apparatus.

15. Development takes place without amnion and allantois.

None of these characters is absolutely diagnostic, except 1 (_c_), and
this applies only to the Anura and most of the Stegocephali.

{5}Numbers 1 (_b_), 1 (_c_), 2, 3, 4 and 12 separate the Amphibia from
the Fishes.

Numbers 1, 6 (_b_), 7, 8, 9, 11, 13, 15 separate them from the
Reptiles, Birds, and Mammals.

Number 2 separates them from the Fishes, Reptiles, and Birds.

Number 5 separates them from the Mammals.

Number 6 (_a_) separates them from the Fishes (excl. Dipnoi), Birds and
Mammals.

We can, therefore, very easily define all the Amphibia, both recent and extinct, by a combination of the characters enumerated above. For instance, by the combination of numbers 2, 3 or 4 with either 7, 8, 9, 11, 13 or 15.

_Amphicondylous Anamnia_ would be an absolutely correct and all-sufficient diagnosis, but it would be of little use in the determination of adult specimens; and the tetrapodous character is of no avail for Apoda. _Amphicondylous animals without an intracranial hypoglossal nerve_ is a more practical diagnosis.

In the case of living Urodela and Anura the absence of any scales in the skin affords a more popular character; it is unfortunately not applicable to the Apoda, many of which possess dermal scales, although these are hidden in the imbricating transverse rings of the epidermis; and the frequent occurrence of typical scales of both ecto- and meso-dermal composition in many of the Stegocephali forces us to discard the scales, or rather their absence, as a diagnostic character of the class Amphibia. The same applies to the mostly soft, moist, or clammy, and very glandular nature of the skin.

THE POSITION OF THE CLASS AMPHIBIA IN THE PHYLUM VERTEBRATA.–There is no doubt that the Amphibia have sprung from fish-like ancestors, and that they in turn have given rise to the Reptilia. The Amphibia consequently hold a very important intermediate position. It was perhaps not a fortunate innovation when Huxley brigaded them with the Fishes as _Ichthyopsida_, thereby separating them more from the _Sauropsida_ (= Reptilia and Aves), than is justifiable,–perhaps more than he himself intended. The connecting-link, in any case, is formed by the Stegocephali; all the recent Orders, the Apoda, Urodela, and Anura, are far too specialised to have any claims to the direct ancestral connections. The line leading from Stegocephali to fossil Reptiles, notably to such Proreptilia as _Eryops_ and _Cricotus_, and even to the Lepospondylous Prosauria, is extremely gradual, and the steps are almost imperceptible. Naturally, {6}assuming evolution to be true, there must have lived countless creatures which were a "rudis indigestaque moles," neither Amphibia nor Reptilia, in the present intensified sense of the systematist. The same consideration applies equally to the line which leads downwards to the Fishes. But the great gulf within the Vertebrata lies between Fishes and Amphibia, between absolutely aquatic creatures with internal gills and "fins," and terrestrial, tetrapodous creatures, with lungs and fingers and toes. On the side of the fishes only the Dipnoi and the Crossopterygii come into consideration.

The piscine descent of the Amphibia is still proclaimed by the following features.–(1) The possession by the heart of a long conus arteriosus, provided with, in many cases, numerous valves, or at least (Anura) one series at the base, another at the beginning of the truncus where the arterial arches branch off; (2) the strictly symmetrical arrangement of these arches; (3) the trilocular heart is still like that of the Lung-fishes or Dipnoi; (4) the occurrence of as many as four or even five branchial skeletal arches in the larval stage; (5) the glottis is supported by cartilages which themselves are derivatives of posterior visceral arches; (6) the development of the vertebrae (Stegocephali and Urodela) from four pairs of arcualia, and the formation of the intervertebral joints by a split across the intervertebral ring of cartilage: this feature is unknown in Reptilia, but it occurs also in _Lepidosteus_, most probably also in _Polypterus_; (7) the hypoglossal still retains the character of a post-cranial or cervical spinal nerve; (8) the presence of lateral sense-organs; (9) the possession of external gills is of somewhat doubtful phylogenetic value, although such gills occur amongst fishes only in Dipnoi and Crossopterygii. It is not unlikely that in the Amphibia these organs owe their origin to entirely larval requirements, while the suctorial mouth of the larvae of the Anura and many fishes has certainly no ancestral meaning, but is a case of convergent development.

The usual diagnoses of the Amphibia contain the statement that they, or most of them, undergo a metamorphosis, or pass through a larval stage. The same applies to various fishes; while, on the other hand, the larval (not ancestral) stage has become permanent in the Proteidae and Sirenidae; and lastly, we cannot well speak of larvae in the viviparous _Salamandra atra_.

{7}THE EVOLUTION OF AN ADEQUATE CLASSIFICATION OF THE AMPHIBIA has been a long process. Even their recognition as a class, separate from, and of equal rank with that of, the Reptilia, was by no means generally accepted until comparatively recent times. A historical sketch of the laborious, often painful, striving for light, in France and Germany, then in England, and lastly in America, is not without interest.

The term _Amphibia_ was invented by Linnaeus for the third class of
animals in his famous "Systema Naturae." It comprises a very queer
assembly, which, even in the 13th edition (1767), stands as follows:–

1. REPTILES PEDATI, with the four "genera" _Testudo_, _Draco_,
_Lacerta_, and _Rana_. _Lacerta_ includes Crocodiles, Lizards, and
Newts!

2. SERPENTES APODES.

3. NANTES PINNATI. Elasmobranchs, Sturgeons, Lampreys, and various
other fishes.

Laurenti, 1768, in a dissertation entitled "Specimen medicum, exhibens
Synopsin Reptilium ...," uses Brisson's term, REPTILES, and divides them
into:–

REPTILIA SALIENTIA, these are the Anura.

GRADIENTIA, namely the Urodela and Lizards.

SERPENTIA, the Snakes and the Apoda.

Brongniart, 1800, "Essay d'une classification naturelle des Reptiles,"[2]
distinguishes:–

CHELONII, SAURII, OPHIDII, BATRACHII; the last for the Frogs, Toads,
and Newts.

Latreille, 1804, "Nouveau Dict. Hist. Nat." xxiv.,[3] accepts the four
Orders of Brongniart's "Reptiles," but clearly separates the fourth
Order, "BATRACHII," from the rest by the following, now time-honoured,
diagnosis: _Doigts des pattes n'ayant pas d'ongles; des branchies, du
moins pendant un temps; des métamorphoses_. But there is not one word
about "Amphibia" in opposition to "Reptilia."

Duméril, 1806, "Zoologie analytique" (p. 90), and "Élémens de l'histoire
naturelle," 1807, divides the "Reptiles batraciens," or "Batracii," into
ECAUDATI and CAUDATI; he also introduces the terms "ANOURES" and
"URODÈLES" as their equivalents; but since these terms appear in the
French form purists do not admit their having any claim to recognition!

Oppel, 1811, "Die Ordnungen, Familien und Gattungen der Reptilien,"
establishes the term APODA for the Coeciliae, and recognises their
affinity to the Ecaudata and Caudata by removing them from the Snakes.

De Blainville, 1816, "Prodrome d'une nouvelle distribution du règne
animal"[4]–

AMPHIBIENS SQUAMIFÈRES. [The Reptilia.]

" NUDIPELLIFÈRES s. Ichthyoides. [The Amphibia.]

{8}Merrem, 1820, "Tentamen systematis Amphibiorum."

PHOLIDOTA. [The Reptilia.]

BATRACHIA: _APODA_.
_SALIENTIA_.
{ Mutabilia [with metamorphosis, _e.g._
_GRADIENTIA_ { Newts.]
{ Amphipneusta [Perennibranchiate Urodeles.]

F. S. Leuckart, 1821, "Einiges ueber die fischartigen Amphibien."[5]

MONOPNOA. [The Reptilia.]

{ with temporary gills: Ecaudata + Caudata pt.
DIPNOA. [The Amphibia] { with permanent gills: "Proteidae," _Menopoma_
{ and _Amphiuma_.

Latreille, 1825, "Familles naturelles du règne animal." The Vertebrata
are divided into _Haematherma_ and _Haemacryma_. These terms for warm and
cold-blooded creatures were later on amended by Owen to _Haematotherma_
and _Haematocrya_. The latter are divided by Latreille as follows:–

REPTILIA. Still including the Coeciliae amongst the Snakes.

AMPHIBIA { Caducibranchiata.
{ Perennibranchiata.

PISCES.

Wagler, 1830, "Systema Amphibiorum."

TESTUDINES, CROCODILI, LACERTAE, SERPENTES, ANGUES, COECILIAE, RANAE,
ICHTHYODI.

RANAE I. _AGLOSSA._

" II. _PHANEROGLOSSA_: 1. Cauda nulla. [The Anura.]

" " 2. Cauda distincta. [The Salamandridae.]

ICHTHYODI I. _ABRANCHIALES._ _Menopoma_ [_Cryptobranchus_] and
_Amphiuma_.

" II. _BRANCHIALES._ [The Perennibranchiate Urodela.]

J. Müller, 1831, "Beiträge zur Anatomie ... der Amphibien."[6]

GYMNOPHIONA, DEROTREMATA, PROTEIDAE, SALAMANDRINA, BATRACHIA.

J. Bell, 1836, Todd's "Cyclopaedia of Anatomy and Physiology," Art.
"Amphibia."

AMPHIPNEUSTA, the Perennibranchiate Urodeles; ANOURA, URODELA;

ABRANCHIA, _Menopoma_ and _Amphiuma_; APODA.

Stannius, 1856, "Handbuch der Zootomie: Anatomie der Wirbelthiere." (2nd
ed.)

AMPHIBIA MONOPNOA. The Reptilia.

AMPHIBIA DIPNOA. 1. URODELA. _PERENNIBRANCHIATA._
_DEROTREMATA_: _Amphiuma_ and _Menopoma_.
_MYCTODERA._[7]
{9} 2. BATRACHIA. _AGLOSSA._
_PHANEROGLOSSA_: Systomata =
Engystomatidae.
Bufoninae. Without manubrium sterni.
Raninae. With manubrium.
Hyloidea. With adhesive finger-discs.
_GYMNOPHIONA._

Gegenbaur, 1859, "Grundzüge der vergleichenden Anatomie."

AMPHIBIA as a separate class, equivalent to that of the REPTILIA, are
divided into the four Orders: _PERENNIBRANCHIATA_, _SALAMANDRINA_,
_BATRACHIA_, and _GYMNOPHIONA_. In the second edition of the
"Grundzüge" (1870) they are divided into _URODELA_, _ANURA_, and
_GYMNOPHIONA_.

Huxley, 1864, "The Elements of Comparative Anatomy."

MAMMALS.
SAUROIDS, subsequently changed into SAUROPSIDA = Reptilia + Aves.
ICHTHYOIDS, " " ICHTHYOPSIDA = Amphibia + Pisces.

Haeckel, 1866, "Generelle Morphologie."

Amphibia. A. PHRACTAMPHIBIA s. Ganocephala = Labyrinthodonta + Peromela
[Apoda].
B. LISSAMPHIBIA s. Sozobranchia = Sozura [Urodela] + Anura.

Cope, 1869.[8]

STEGOCEPHALI, GYMNOPHIDIA, URODELA, PROTEIDEA, TRACHYSTOMATA, ANURA.

Huxley, 1871, "A Manual of the Anatomy of Vertebrated Animals."

Amphibia I. SAUROBATRACHIA [v.d. Hoeven's term] s. URODELA
1. Proteidea.
2. Salamandridae.
II. LABYRINTHODONTA.
III. GYMNOPHIONA.
IV. BATRACHIA s. ANURA.

Boulenger, 1882, "Catalogue of the BATRACHIA GRADIENTIA s. CAUDATA and
BATRACHIA APODA," divides the Caudata simply into: _SALAMANDRIDAE_,
_AMPHIUMIDAE_, _PROTEIDAE_, and _SIRENIDAE_.

1882, "Cat. Batrachia Salientia s. Ecaudata," see p. 140.

Cope, 1890, "Synopsis of the Families of Vertebrata."[9]

CLASS BATRACHIA.
Sub-Class I. STEGOCEPHALI.
Order 1. Ganocephali: _Trimerorhachis_, _Archegosaurus_.
2. Rhachitomi: _Eryops_.
3. Embolomeri: _Cricotus_.
4. Microsauri: _Branchiosaurus_, _Hylonomus_, etc.
{10} Sub-Class II. URODELA.
Order 1. Proteidae: _Proteus_.
2. Pseudosauria. [All the rest of the Urodela +
Coeciliidae.]
3. Trachystomata: Sirenidae.
Sub-Class III. SALIENTIA.

P. and F. Sarasin, 1890, "Zur Entwicklungsgeschichte der Ceylonesischen
Blindwühle, Ichthyophis glutinosa."[10]

Sub-Class I. ARCHAEOBATRACHI s. STEGOCEPHALI.
II. NEOBATRACHI.
Order 1. _URODELA._
_a_. Salamandroidea. [The Urodela.]
_b_. Coeciloidea = Amphiumidae + Coeciliidae.
2. _ANURA._

The classification adopted in this volume is as follows:–

CLASS AMPHIBIA.
Sub-Class I. Phractamphibia.
Order I. Stegocephali Lepospondyli.
Sub-order 1. Branchiosauri.
Sub-order 2. Aistopodes.
Order II. Stegocephali Temnospondyli.
Order III. Stegocephali Stereospondyli.
Sub-Class II. Lissamphibia.
Order I. Apoda.
Order II. Urodela.
Order III. Anura.
Sub-order 1. Aglossa.
Sub-order 2. Phaneroglossa.

{11}CHAPTER II

SKELETON OF URODELA AND ANURA–SKIN–COLOUR-CHANGING MECHANISM– POISON-GLANDS–SPINAL NERVES–RESPIRATORY ORGANS–SUPPRESSION OF LUNGS– URINO-GENITAL ORGANS–FECUNDATION–NURSING HABITS–DEVELOPMENT AND METAMORPHOSIS

SKELETON OF THE URODELA

THE VERTEBRAL COLUMN.–The number of vertebrae is smallest in the terrestrial, greatest in the entirely aquatic forms, and is exceptionally large in the eel-shaped _Amphiuma_. In the following table the sacral vertebra is included in those of the trunk.

Trunk. Tail.
_Siren lacertina_ 22 35 +
_Necturus maculatus_ 19 29
_Proteus anguinus_ 30 28 +
_Cryptobranchus alleghaniensis_ 20 or 21 24 +
_C. scheuchzeri_ 21
_C. japonicus_ 22 22 to 26
_Amphiuma means_ 63 35 +
_Amblystoma tigrinum_ 17 or 16 32 +
_Salamandra maculosa_ 17 27
_Triton cristatus_ 17 36
_Triton taeniatus_ 14 or 15 36 +
_Triton palmatus_ 14 23 to 25
_Salamandrina perspicillata_ 15 32 to 42
_Spelerpes fuscus_ 16 23

The vertebrae of the Urodela and those of the Apoda differ from those of all the other Tetrapoda[11] by possessing no special centra or bodies. That part which should correspond with the centrum is formed either by the meeting and subsequent complete co-ossification of the two chief dorsal and ventral pairs of arcualia {12}(tail-vertebrae), or entirely by the pair of chief dorsal arcualia. There is consequently no neuro-central suture. Moreover, the central region of each vertebra is strongly pinched in laterally, widening towards the ends. Another feature of the vertebral column of the Urodela is the possession of a considerable amount of intervertebral cartilage, by which the successive vertebrae are held together. This cartilage does not ossify, and it either remains continuous, serving in its entirety and owing to its flexibility as a joint, or it becomes more or less imperfectly separated into a cup and ball portion, the cup belonging to the posterior end of the vertebra. Such joints are called opisthocoelous, and occur in the Desmognathinae and Salamandrinae. In the adult the cup and ball frequently calcify, and the chorda dorsalis or notochord is completely destroyed. Those vertebrae between which the intervertebral cartilage remains unbroken, are called amphicoelous, since in them, most obviously in macerated or dried skeletons, the vertebrae appear hollowed out at either end. In such amphicoelous vertebrae a considerable amount of the chorda always remains, running in an unbroken string through the whole length of the vertebral column. Towards adult life the chorda becomes constricted, and is ultimately squeezed out or destroyed, in the middle of the vertebra, by the invasion of cartilage from the chief arcualia. This intravertebrally situated cartilage has been described erroneously as chordal cartilage.

The development of the vertebrae proceeds as follows. First appear a pair of basidorsalia and a pair of basiventralia (Fig. 1, 1, B.D, B.V), blocks of cartilage, imbedded in and resting upon the thin sheath of the chorda dorsalis. Next appears a pair of interdorsal blocks, immediately behind the basidorsals; and somewhat later appears a pair of interventral blocks. These four pairs of cartilages or "arcualia" each meet, above or below the chorda, and form semi-rings, which again by extending upwards or downwards fuse into complete rings, in such a way that the interdorsal and interventral elements form the intervertebral mass spoken of above. The basidorsals fuse with the basiventrals, and form the body of the vertebra, the fusion being effected chiefly by the calcification and ossification of the lateral connecting portion of the skeletogenous layer. The basidorsalia form the neural arches with their unpaired short spinous or neural, and the paired anterior and posterior zygapophysial processes. Concerning the {13}basiventralia we have to distinguish between the trunk and the tail. In the latter they produce a pair of ventral outgrowths or haemapophyses, which ultimately enclose the caudal blood-vessels. In the trunk the basiventral blocks of cartilage are suppressed; they appear in the early larvae, but disappear during or even before metamorphosis.

Towards the end of the tail the vertebrae diminish in size, and their constituent cartilages assume a more and more indifferent shape, until they become confluent into a continuous rod of cartilage, resembling in this respect the Dipnoi and Holocephali. A periodical revival of this rod, at least of its connective tissue, appears in the tail-filament of the male _Triton palmatus_ during the breeding-season.

The first vertebra, called the atlas, because it carries the head, is remarkable for the possession of an odontoid process. The latter is formed by a pair of cartilages and represents part of a vertebra, the dorsal portion of which seems to have been added to the occipital part of the cranium.

{14}All the trunk-vertebrae, with the exception of the atlas, carry ribs, at least vestiges thereof. Owing to the early disappearance of the basiventral cartilages the capitular portions of the ribs are much reduced, and are mostly represented by strands of connective tissue only. The ribs develop therefore occasionally at some distance from the vertebral column, and that portion of the rib which in the metamorphosed young newt looks like the capitulum is to a great extent really its tuberculum. Witness the position of the vertebral artery, which still indicates the true foramen transversarium. The homologies of these parts are still more obscured by the fact that a new process grows out from the rib, by which the latter gains a new support upon a knob of the neural arch. Thus an additional foramen is formed, sometimes confounded with the true transverse canal. The meaning which underlies all these modifications is the broadening of the body, the ribs shifting their originally more ventral support towards the dorsal side. The whole process is intensified in the Anura; it is an initial stage of the notocentrous type of vertebrae. The transverse ossified processes of the adult are often much longer than the vestiges of the ribs themselves, and are somewhat complicated structures. They are composed first of the rib-bearing cartilaginous outgrowths of the neural arches; secondly, of a broad string of connective tissue which extends from the ventro-lateral corner of the perichordal skeletogenous layer to the ribs.

The SHOULDER-GIRDLE is extremely simple. It remains almost entirely cartilaginous, and the three constituent elements are not separated by sutures. Ossification is restricted to the base of the shaft of the scapula, and may extend thence over the glenoid cavity. The coracoids are broad, loosely overlap each other, and are "tenon and mortised" into the triangular or lozenge-shaped {15}cartilaginous sternum, which latter has no connection with the ribs. The precoracoid is a large, flat process, directed forwards, not meeting its fellow; it is absent in _Siren_.

The humerus articulates with both radius and ulna, and these two bones of the forearm remain separate. The elements which compose the wrist and hand exhibit an almost ideally simple arrangement, slightly varied by the frequent fusion of two or more neighbouring carpalia into one, and by the reduction of the number of fingers. Most frequently the intermedium and the ulnar carpal element fuse together, and there is more often one centrale instead of two. The wrist and hand of the Urodela represent, however, no longer the entirely primitive pentadactyle type, owing to the loss of one finger together with its metacarpal and carpal element. Comparison with the Anura makes it probable that the Urodela have lost the pollex, their four fingers being consequently the 2nd, 3rd, 4th, and 5th. _Siren_ has four or three fingers; _Proteus_ has only three fingers and three large compound carpal cartilages. In _Amphiuma_, with either three or two fingers, the ulnare, intermedium, and carpale are fused together, the radiale with the neighbouring carpale. The number of phalanges in the four-fingered species is generally 2, 3, 3, 2 respectively.

The PELVIC GIRDLE.–The ilium stands vertically to the vertebral axis, slanting slightly forwards and downwards. It is attached by means of a rib to only one vertebra, and this ilio-sacral connection is acetabular in its position, _i.e._ it lies in the same transverse plane with the acetabulum, in other words vertically above it. The ventral portion of the pelvis is formed by one large continuous mass, the united pubo-ischia, the anterior or pubic portion of which extends forwards in the shape of a broad triangle (_Necturus_) or as a slender, stalked, Y-shaped cartilage, the epipubis, which is often movably jointed at its base. The lateral portion of the pubic cartilage is always perforated by the nervus obturatorius. Ossification is restricted to the ischium and to the middle of the shaft of the ilium. The acetabular fossa for the femur is closed. The tibia and fibula remain separate. The foot is still more primitive than the anterior extremity, as the majority of Urodela possess the full complement of five toes, with 2, 2, 3, 3, 2 phalanges respectively. Concrescence of the tarsalia applies most frequently to the fourth and fifth distal {16}and to the two centralia; exceptional, for instance, in _Cryptobranchus japonicus_, are as many as three centralia, but this is an individual, even a one-sided variation, as shown for instance by a specimen in the Cambridge Museum. Loss of the fifth toe occurs sporadically in genera of different groups, namely, in _Salamandrella_, _Batrachyperus_, _Salamandrina_, _Necturus_, _Manculus_, _Batrachoseps_. In _Amphiuma_ the number is reduced to three or two; in _Proteus_ to two; and in _Siren_ the hind limbs, with their girdle, are altogether absent. Lastly, in some species of _Spelerpes_ and _Batrachoseps_ both fore and hind limbs have become so small as to be practically without function, parallel cases being found among various Scincidae and other Lizards.

The HYOID APPARATUS is still very primitive in many, especially in larval, Urodela. Besides the hyoid there are as many as four pairs of branchial arches, which, however, decrease in size and completeness, so that the last two have lost their connection with the median copular piece, and become attached in various ways to the second branchial arch. This is the arrangement apparently in all larvae, but four pairs of branchials persist in the adult _Siren_, _Amphiuma_, and _Cryptobranchus alleghaniensis_. The whole branchial apparatus is reduced to three pairs of arches in _Necturus_ and _Proteus_, to two in the adult _Cryptobranchus japonicus_ and in the Salamandridae. Of considerable interest is the vestige of a fifth pair of arches in the larvae of _Triton_ and _Salamandra_, in the shape of a pair of tiny cartilages, which lie in front and on each side of the opening of the trachea, and give rise to the formation of the laryngeal cartilages, better developed in the higher Vertebrata.

The following are noteworthy characters of the SKULL OF URODELA. The articulation of the skull with the vertebral column is not always effected entirely by the two condyles of the lateral occipital bones, but the median basal cartilage often possesses a pair of facets for the odontoid-like process of the first vertebra; such additional facets are perhaps best developed in _Cryptobranchus_ and in the Salamandrinae.

The middle portion of the primitive cranium, from the exit of the optic nerve to the ethmoid cartilage, is formed by a pair of separate bones, the orbito-sphenoids. The parietal and frontal bones remain separate. One or more periotic bones exist, besides the prootic, in the aquatic families.

{17}A pair of prefrontal bones is present in most Salamandridae, e.g. _Salamandra_, _Triton_, _Amblystoma_, especially in the larva, and in _Cryptobranchus_; these bones are absent in _Amphiuma_, _Necturus_, _Proteus_, and _Siren_.

The lacrymalia are still separate in some Amblystomatinae, e.g. _Ranidens_ and _Hynobius_. A pair of nasalia are generally present, but are absent in _Necturus_, _Proteus_, and _Siren_. The parasphenoid is furnished with teeth in the Plethodontinae and Desmognathinae.

Separate palatine bones exist in _Necturus_ and _Proteus_, and in the larva of _Amblystoma_, but in the adult form they fuse with the vomers, producing the vomero-palatines characteristic of the majority of Urodela.

{18}The pterygoid bones are most fully developed, so as to reach the vomero-palatines, in the Amblystomatinae, in _Necturus_, and in _Proteus_; they are reduced, so as to leave a gap, in _Cryptobranchus_, and still more in the Salamandrinae; they are absent in _Amphiuma_ and in _Siren_.

The quadrates are directed forwards in _Necturus_, _Proteus_, and _Siren_, while in the other Urodela they extend transversely and almost horizontally. The hyomandibular remnant, the so-called operculum, is small, and forms a plate which fits into the fenestra ovalis, extending as a ligamentous process upon the quadrate.

The quadrato-jugal elements are reduced to ligaments. In many Salamandrinae the large orbito-temporal space is divided into an orbital and a temporal fossa by an arch which is formed by the meeting of two corresponding processes from the squamosal and frontal bones respectively. This bridge is rarely bony (_Salamandrina_, _Triton_), mostly ligamentous;–apparently a reminiscence of the Stegocephalous condition. The two premaxillary bones are liable to fuse into one, for instance in _Cryptobranchus_, generally in adult Tritons. They are most reduced, and are toothless, in _Siren_.

The two maxillary bones are absent only in _Necturus_, _Proteus_, _Typhlomolge_, and _Siren_. Their posterior end is frequently free, loosely connected by ligaments with the pterygoid in _Cryptobranchus_; or with the distal portion of the quadrate, and in this case either just touching it (_Tylototriton_), or forming a broad junction (_Pachytriton_).

Each half of the lower jaw consists of a dentary, articular and angulo-splenial. The splenial remains as a separate element in _Siren_; in others only during the larval period. There are no mento-Meckelian elements.

SKELETON OF THE ANURA

THE VERTEBRAL COLUMN.–The distinctive peculiarities of the vertebrae of the Anura are that they are notocentrous, and that about a dozen of them are modified and fused into an os coccygeum. The whole column is the most specialised found in the Vertebrata; and various stages are rapidly hurried through and obscured caenogenetically during the embryonic development. Paired cartilages appear on the dorsal side of the thin chordal sheath, and whilst tending to enclose the spinal cord in a {19}canal, their bases grow head- and tail-wards into what will ultimately become the intervertebral region. This extension of cartilage leads to a fusion with that of the next following pair of arches, so that the axial column at this early stage consists of a right and left longitudinal ridge of cartilage which sends off dorsal processes, neural arches, in metameric succession. Next, the intervertebral cartilage increases in such a way as to constrict the chorda either laterally (_Rana_) or obliquely from above downwards and inwards (_Bufo_, _Hyla_). We recognise in this cartilage the interdorsalia. Ventral arcualia are late and much obscured. There is scarcely any cartilage which could represent the interventralia, the intervertebral cartilage being almost entirely made up of the interdorsalia. These fuse together and form a disc or nodule, which later fuses either with the vertebra in front, and in this case fits into a cup carried by the vertebra next behind (procoelous vertebrae), or the knob is added to the front end of the vertebra, fitting into a cup formed by the tail end of the vertebra next in front (opisthocoelous vertebrae). Much later than the two longitudinal dorsal bands there appears on the ventral side an unpaired band in which appear metamerically repeated swellings of cartilage, likewise unpaired. These swellings become confluent, in a way similar to that which produced the dorsal bands, and form the unpaired ventral band of cartilage, the hypochordal cartilage of some authors. The swellings in this band, equivalent to the basiventralia, become semilunar in a transverse view, their horns tending upwards towards the basidorsal cartilages, but there is no actual meeting. Both dorsal and ventral elements are, however, joined together and form the chief portion of the vertebrae, owing to the rapidly proceeding calcification and later ossification of the all-surrounding "membrana reuniens" or skeletogenous layer so far as that is not cartilaginous.

Procoelous vertebrae exist in the overwhelming majority of Anura; opisthocoelous are those of the Aglossa, the Discoglossidae, and of some Pelobatidae. The systematic value of this pro- or opistho-coelous character has been much exaggerated. We have seen that the centra of the vertebrae of the Anura are formed entirely by the interdorsal elements, hence the term "notocentrous," and these centra sometimes remain in adult specimens of _Pelobates_ as separately ossified and calcified pieces, {20}not fused with the rest of the vertebrae. This important discovery has been made by Boulenger, but Stannius had previously mentioned a specimen of _Pelobates_ in which the second and fourth vertebrae are biconvex, the third, sixth, and eighth biconcave. Moreover, since the sacral vertebra, generally the ninth, in all the Anura is invariably biconvex, the eighth being biconcave in the procoelous families, opisthocoelous like the remaining seven vertebrae in the other families, it is not difficult to imagine that in the Anura the production of pro- or opistho-coelous vertebrae depends simply upon the centra or articulating knobs happening to fuse either with the hind or the front end of the vertebrae. This must of course ultimately be determined by a mechanical problem of motion.

A second type of the vertebrae amongst the Anura is the epichordal type, an exaggeration in degree of the notocentrous tendencies of the more usual perichordal arrangement. It shows, namely, the almost complete suppression of all the ventral cartilaginous elements, so that the chorda remains for a long time on the ventral surface of the axial column in the shape of a flattened longitudinal band. These two types are not unconnected. The suppression of the ventral elements applies most typically to the trunk region, while hypochordal cartilage exists in the anterior cervical vertebrae, and above all in the coccyx. Typically epichordal are the vertebrae of _Pipa_, _Xenopus_, _Bombinator_, _Pelobates_, _Discoglossus_ and _Alytes_. It is significant that the epichordal often coincide with opisthocoelous vertebrae, and still more suggestive is the fact that _Bombinator_ is eminently aquatic, _Pipa_ and _Xenopus_ entirely so, having lost the tympanum, at least externally. The epichordal feature is not necessarily indicative of relationship. It has probably been developed independently in various groups, in correlation with a resumption of aquatic life. Various genera of Pelobatidae and most likely some Cystignathidae, e.g. _Pseudis_, will not improbably connect the two types and their several correlated features, for instance, the frequent reduction of the tympanic cavity.

The os coccygeum has retained rather primitive features in so far as much dorsal and ventral cartilage is developed; but this has almost entirely lost its metameric arrangement, and the posterior half of the coccyx is formed chiefly by the ventral mass of cartilage, while the dorsal elements are more or less reduced. {21}Only two vertebrae, generally the tenth and eleventh of the whole column, are clearly visible, each being composed of a pair of dorsal and a pair of ventral cartilaginous blocks. The sacral vertebra articulates with the coccyx by one or two convexities, but in the Aglossa, in some Pelobatidae, and a few others, the coccyx is fused with the sacral vertebra. Beyond the first and second component vertebrae of the embryonic coccyx, the cartilage is continued in the shape of two dorsal, and one ventral, bands, which soon fuse with each other. Dorsally this cartilage surrounds the spinal cord; the latter degenerates towards the end of the tadpole-stage, leaving, however, the empty spinal canal. The chorda, completely surrounded by cartilage, persists into the post-larval stage, but is destroyed long before the creature attains maturity. Ultimately the whole coccyx ossifies.

The tail proper, namely that portion which is absorbed during the metamorphosis, remains throughout its existence in an apparently primitive condition. The chorda dorsalis and the spinal cord extend through its whole length, surrounded by continuous connective tissue without any cartilage; in fact it represents a piece of typical vertebral column before the appearance of cartilage. The reduction of this swimming organ begins at the hind end.

The vertebral column of the adult.–The first vertebra (we will call it the atlas since it carries the skull) is not, as in the Urodela, provided with an odontoid process. It articulates by two cups with the condyles of the occiput. In some Anura it co-ossifies, rather incompletely, with the second vertebra, regularly in the fossil _Palaeobatrachus_, often in _Ceratophrys_, _Breviceps_, and occasionally in _Pelobates_, _Bufo_, _Rana_, and _Xenopus_. This is, however, no justification for looking upon the first vertebra as a complex of two vertebrae, although the atlas is frequently very thick and broad, and even carries, in the Aglossa, considerable lateral wings or diapophyses. Those of the trunk-vertebrae are often very long, acting thereby as substitutes for ribs which are absent, except on the second, third, and fourth vertebrae of the Discoglossidae, and on the second and third of the Aglossa. In the adult Aglossa these ribs fuse with the processes which carry them.

The diapophyses of the sacral vertebra carry no ribs, the ilia being attached to them directly. They are either cylindrical {22}as in the Ranidae and Cystignathidae, or they are more or less dilated as in all the other families, most strongly in the Pelobatidae and the Aglossa. In some members of the large sub-family of the Cystignathidae the otherwise cylindrical diapophyses are slightly dilated.

The sacrum is formed by the ninth vertebra, but there are a few interesting exceptions. _Pelobates_, _Pipa_, and _Hymenochirus_ possess two sacral vertebrae; and, neglecting individual abnormalities, these three genera form the only exception amongst recent Amphibia. In the three genera the coccyx is fused with the second sacral vertebra, and such a fusion occurs elsewhere normally only in _Bombinator_ with its single sacral vertebra. The morphologically oldest condition is normally represented by _Pelobates_, the sacral vertebrae being the tenth and ninth. One case has been recorded by Boulenger of _Bombinator pachypus_ "with eleven segments," the last carrying the ilium. Individual lop-sided abnormalities have been described in _Bombinator_ and _Alytes_, where the right ilium articulated with the tenth, the left ilium with the ninth vertebra. This shifting forwards of the ilium to the extent of one metamere has been continued further in _Pipa_, in which the sacrum is formed by the ninth and eighth vertebrae, their diapophyses fusing on either side into extra broad wing-like expansions. In old specimens of _Palaeobatrachus fritschi_ the seventh vertebra is in a transitional condition, the ilium being carried by the ninth and eighth, and slightly also by the diapophyses of the seventh vertebra; and in _P. diluvianus_ the {23}diapophyses of all these vertebrae are united into one broad plate to which the ilia are attached. Lastly, in _Hymenochirus_ the first sacral is the sixth vertebra, and this creature has thereby reduced the pre-sacral vertebrae to the smallest number known.

This shifting forwards of the iliac attachment implies the conversion of original trunk into sacral vertebrae, and the original sacral vertebra itself becomes ultimately added to the urostyle. The second sacral, the tenth of _Pelobates_, the ninth of _Pipa_, and the tenth on the right side of the abnormal _Bombinator_, are still in a transitional stage of conversion. In Discoglossidae the tenth is already a typical post-sacral vertebra, and is added to the coccyx, but it still retains distinct, though short, diapophyses. In the majority of the Anura the tenth vertebra has lost these processes, and its once separate nature is visible in young specimens only. In _Bombinator_ even the eleventh vertebra is free during the larval stage. In fact the whole coccyx is the result of the fusion of about twelve or more vertebrae, which from behind forwards have lost their individuality. We conclude that originally, in the early Anura, there was no coccyx, and that the ilium was attached much farther back; and this condition, and the gradual shifting forwards, supply an intelligible cause of the formation of an os coccygeum. The fact that the sacral vertebrae of the Anura possess no traces of ribs as carriers of the ilia, is also very suggestive. The ilia have shifted into a region, the vertebrae of which had already lost their ribs. By reconstructing the vertebral column of the Anura, by dissolving the coccyx into about a dozen vertebrae, so that originally, say the twenty-first vertebra carried the ilia, we bridge over the enormous gap which exists between the Anura and Urodela. That whole portion of the axial continuation behind the coccyx, more or less coinciding with the position of the vent, is the transitional tail.

The disappearance of both notochord and spinal cord, and the conversion of the cartilaginous elements into a continuous rod in the case of the os coccygeum, find an analogy in the hinder portion of the tail of Dipnoi and Crossopterygii, and in the tail-end of most Urodela, portions which are not homologous with the os coccygeum. The term urostyle should be restricted to such and similar modifications of the tail-end, and this latter happens to be lost by the Anura during metamorphosis.

{24}Strictly speaking, or rather in anatomical parlance, the Vertebrate tail begins with the first post-sacral vertebra. In the Anura that portion of the whole tail has retained most cartilage, and has become the coccygeum, which is required as a "backbone" for the often enormous belly. This requirement is an outcome of the great shortening of the trunk proper (if the trunk be defined as ending with the pelvic region), and this shortening of the trunk is again intimately connected with the jumping mechanism, enlargement of the hind-limbs, elongation of the ilia, and throwing the fulcral attachment forwards as much as possible. The pre-acetabular ilio-sacral connection is carried to the extreme in the Anura.

The SHOULDER-GIRDLE and "sternum" are more complete than in the Urodela, there being also a pair of clavicles, fused with the precoracoidal bars. The whole apparatus presents two types. In the arciferous type the coracoids and precoracoids retain a great amount of cartilage in their distal portions, and these cartilages (the epicoracoids of some authors) overlap each other movably on one another, the right usually lying ventrally upon the left. The epicoracoidal cartilage of each side, by connecting the distal end of the coracoid with the precoracoid of the same side, forms an arc, hence "arciferous." In the firmisternal type the epicoracoidal cartilages are much reduced, and, instead of overlapping, meet in the middle line and often fuse with each other, forming thereby a firm median bar, which connects the ventral ends of the precoracoids with those of the coracoids. This type is morphologically the higher and more recent, and passes in the larval stage through the arciferous condition. It is restricted to the Ranidae, Engystomatinae, and Aglossa. Although these two types afford an excellent distinctive character for the main divisions of the Anura, they are to a certain extent connected by intermediate forms in such a way, that, for instance, in _Bufo_ and among Cystignathidae in _Ceratophrys_, the two opposite epicoracoidal cartilages begin to unite at the anterior end.

In many Engystomatinae the precoracoids together with the clavicles are much reduced, sometimes to thin ligaments, being in this case mostly curved back and lying closely against the coracoids; or they may be lost completely. Very rarely the precoracoidal bars are actually much stronger than the coracoids, {25}and the median symphysial bar of cartilage is lost; this is the case in _Hemisus_.

The scapula is always large and curved into transverse, dorsally broadening blades, the dorsal greater portion of which, the so-called supra-scapula, does not ossify but calcifies.

It is very doubtful if the Anura possess a true sternum, if by sternum we understand a medio-ventral apparatus which owes its origin to the ventral portions of ribs. The so-called sternal apparatus of the Anura consists of two pieces. One, anterior, variously named episternum, presternum, or omosternum, rests upon the united precoracoids and extends headwards, being either styliform or broadened out. Sometimes it is partly ossified, with a distinct suture at its base; this is the case especially in the Firmisternia; in many Arcifera the omosternum remains cartilaginous and is continuous, without a sutural break, with the cartilage of the precoracoids, indicating thereby its genetic relation to the shoulder-girdle. Hence _omosternum_ is the {26}preferable name. It is frequently much reduced, even absent, for instance in most Bufonidae and in the Engystomatinae. The posterior so-called sternal part may be termed _metasternum_. It forms the posterior counterpart of the omosternum. It is attached behind to the epicoracoidal cartilages, or fusing with them forms their posterior continuation. It appears mostly in the shape of a style, which is frequently ossified, and broadens out behind into a cartilaginous, partly calcified blade. In the Discoglossidae only it diverges backwards into two horns, assuming a striking resemblance to the typical xiphisternum of the Amniota. In young Anura the metasternal cartilage is intimately connected with the pericardium, an indication of its being derived not from ribs but from the shoulder-girdle.

The glenoid cavity is always formed by the coracoids and by the scapula, but the precoracoid often takes part in its formation, for instance in Bufonidae, Hylidae, and Discoglossidae.

In the FORE-LIMB the humerus has a crest, stronger in the males than in the females; it assumes extraordinary strength in some Cystignathidae, notably in the male _Leptodactylus_. Radius and ulna are fused into one bone. The carpalia are originally nine in number: radiale, ulnare, two centralia, and five carpalia distalia, the fifth of which is reduced to a tiny nodule or to a ligamentous vestige. The primitive condition still prevails in the Discoglossidae. In most of the other Anura the fourth and third distal carpalia, in any case very small, fuse with the enlarged ulnar centrale; the radial centrale comes, in the Bufonidae and Pelobatidae, into contact with the radius, so that the forearm articulates with three elements as in the Urodela, but with this difference, that the intermedium of the Urodela has been lost by the Anura. There are five metacarpalia and five fingers, but the elements of the first or thumb are nearly vestigial, so that the pollux is reduced to one or two nodules, scarcely visible externally. The normal number of the phalanges of the second to fifth fingers is 2, 2, 3, 3. The distal phalanges are generally straight, either pointed or expanded or with Y or T-shaped ends; but in the Hylidae, in _Hylambates_ amongst the Ranidae, and in _Ceratohyla_, one of the Hemiphractinae, the terminal phalanges are produced into curved claws which support the adhesive finger-discs. There are, however, many genera of different families, which possess finger-discs and have no claw-shaped {27}phalanges. The Hylidae, and many of the climbing members of the Ranidae with adhesive discs, possess an extra skeletal piece intercalated between the last and last but one phalanges of the fingers and toes. This piece, a mere interarticular cartilage in _Hyla_, is in the following Raninae developed into an additional phalanx, so that their numbers are 3, 3, 4, 4 in the hand and 3, 3, 4, 5, 4 in the foot: _Cassina_, _Hylambates_, _Rappia_, _Megalixalus_, _Rhacophorus_, _Chiromantis_, _Ixalus_, and _Nyctixalus_. All the other Ranidae are without this additional phalanx, irrespective of the presence or absence or size of digital expansions.[12]

The PELVIC GIRDLE looks like a pair of tongs (see Fig. 4, p. 22). The ilium is enormously elongated and is movably attached to the sacral diapophyses. This connection is always pre-acetabular in position. The ilium and ischium co-ossify completely, and make up nearly the whole of the pelvis; the pubis is very small, and remains cartilaginous unless it calcifies. It rarely possesses a centre of ossification, for instance in _Pelobates_, where the osseous nodule is excluded from the acetabulum, recalling certain Labyrinthodonta, whose ossa pubis likewise do not reach that cavity. The latter is open or perforated in young Anura and remains so in the Discoglossidae, but in the others it becomes closed up as in the Urodela. The ventral halves of the pelvis, besides forming a symphysis, closely approach each other, just leaving room for the passage of the rectum and the urino-genital ducts.

The HIND-LIMBS are in all cases longer than the fore-limbs. The femur is slender, the tibia and fibula are fused into one bone. The tarsus is much modified by the great elongation of the two proximal tarsalia (there being no intermedium) into an astragalus and a calcaneum, both of which fuse together distally and proximally, or completely as in _Pelodytes_; in the latter case the limb assumes a unique appearance, since it consists of three successive and apparently single bars of nearly equal length. The other tarsal elements, especially the more lateral ones, are practically reduced to pads. The Anura have thereby acquired two well-marked joints, one cruro-tarsal, the other tarso-metatarsal; this shows a high stage of specialisation in comparison with the Urodelous and Stegocephalous type of still undefined joints.

{28}The Anura possesses five well-developed toes with normally 2, 2, 3, 4, and 3 phalanges, and the rudiments of a sixth digit, the so-called prehallux, which consists of from two to four pieces, including the one which represents its metatarsal. This prehallux, as a vestige of a once better developed digit, is exactly like the elements on the radial side of the wrist, which, we are certain, are the remnants of a once complete finger, namely the pollex. The only weighty difficulty against its interpretation as a prehallux lies in the fact that hitherto no six-toed Stegocephali have been found; but the fact that there are no Stegocephali known with more than four fingers could be used as an argument against there being a pollex-vestige in recent Anura with just as little reason.

The SKULL of the Anura differs from that of the other recent Amphibia in the following features:–

The orbital region of the primitive cranium remains cartilaginous, but further forward the cranial cavity is closed by the unpaired sphenethmoid, which forms a ring round the anterior portion of the brain-cavity, hence called "os en ceinture" by some anatomists. The frontals and parietals fuse into one pair of fronto-parietal bones, and these again can fuse together in the middle line; as in Aglossa and _Pelobates_. The palatal portion of the palato-quadrate cartilage is complete, reaching forwards to the sides of the ethmoid region. The curved arch, formed by this cartilage, is covered by the following bones: (1) the quadrato-jugal, reduced to a thin splint which connects the quadrate and squamosal with the posterior end of the maxilla; (2) the pterygoid, always strong, extending from the distal inner corner of the quadrate to the maxilla, sometimes also to the palatine, and with a broad, median process to the parasphenoid, this process covering ventrally most of the otic region; (3) the palatines, which vary considerably in shape and size; they are placed transversely and meet in the middle line; in _Bombinator_ and _Pelodytes_ they are absent.

The quadrates are directed transversely and backwards, in conformity with the wide gape of the mouth. The squamosal is always well developed, covering the whole of the quadrate on its outer side; it has a forwardly directed process which ends freely in _Rana_, meets a corresponding process of the maxilla and forms a bony arch with it in _Discoglossus_, _Pelobates_, and others, or {29}is scarcely developed at all, for instance in _Bufo_. In _Pelobates cultripes_ the squamosal is very wide and forms a junction with the fronto-parietals, thus producing a broad bridge across the temporal fossa.

The nasal bones are large and meet in the middle line. Frequently they leave a space between them and the diverging anterior portion of the fronto-parietals, through which gap appears part of the dorsal surface of the ethmoid cartilage. A fontanelle between the frontals occurs in most Hylidae, many Cystignathidae, some few Bufonidae, in _Pelodytes_ amongst the Pelobatidae, and in the Discoglossidae.

The tympanic cavity is bordered in front, above, and below by the squamosal and quadrate, behind by the musculus depressor mandibulae, internally by the otic capsule, and by the cartilage of the cranium between this and the lateral occipital bone. The cavity communicates, however, by the wide and short Eustachian tube with the mouth, the passage being bordered anteriorly by the pterygoid, posteriorly by soft parts. Partly imbedded in these soft tissues is the styloid process or stylohyal, which is attached to the cranium, mostly behind the otic region, and is continued downwards into the anterior horn of the hyoid. The whole partly cartilaginous, ligamentous, and osseous string is, in fact, the entire ventral half of the hyoid arch, while the dorsal half or hyomandibular portion of this, the second visceral arch, is modified into the columellar or auditory chain. The inner end of this chain, the stapes, is inserted into and around the fenestra ovalis of the otic capsule, while the outer end is somewhat T-shaped, and is loosely attached to or near the upper rim of the tympanic ring and to the middle of the tympanic disc. In many Anura this terminal bar can be seen from the outside. The middle portion of the columellar chain is ossified, the rest remains cartilaginous. But the whole chain exhibits various modifications in different genera, especially in the number and the extent of the processes sent out by the outer cartilaginous portion; these are attached in various ways to the tympanum and its rims. The tympanic disc is carried by a cartilaginous ring, which rests against a special process sent out by the quadrate, and is probably itself a differentiation of this element.

In some very aquatic genera, but also in _Pelobates_, the {30}tympanic cavity is much reduced, for instance in _Bombinator_, _Liopelma_. In _Batrachophrynus_ not only the cavity, but also the Eustachian tubes are suppressed. In the Aglossa only the two tubes are united into one short but wide median canal, opening at the level of the pterygoids on the roof of the mouth.

The lower jaw is remarkable for the possession of mento-Meckelian cartilages, absent only in the Aglossa and Discoglossidae. At first they are much longer than the rest of the jaw; during the larval life they indeed form the functional jaw, and they are now covered with horny sheaths instead of teeth. Owing to the absence of teeth on them, these mento-Meckelian cartilages are later not invested by bone, although in many Anura they ultimately ossify, either retaining their separate nature or fusing partly with the dentary bones. The bulk of the lower jaw, the Meckelian cartilage, becomes invested by the dentary, a small articulare, and an inner angulare, while a splenial element is absent. The dentary itself is mostly reduced to a small dentigerous splint, while the angulare forms by far the greater part of the bony jaw.

Teeth are more restricted in their occurrence than in the Urodela. On the jaws they always stand in one row. With the exception of the Hemiphractinae, Amphignathodontinae, Ceratobatrachinae, and Genyophryninae, no recent Anura carry teeth on the lower jaw, and even in these genera they are mostly much reduced in size and firmness, having all the appearance of vanishing structures. The premaxillae and maxillae are frequently furnished with teeth, except in the Dendrobatinae, Genyophryninae, Engystomatinae, Dendrophryniscinae, Bufonidae, _Pipa_, and _Hymenochirus_. The vomers mostly carry a series of teeth on their posterior border; when these teeth are absent, as in many species of _Bufo_, a kind of substitute sometimes occurs on the palatines in the shape of a row of tuberosities. The palatines carry teeth in Hemiphractinae. The parasphenoids are rarely toothed, _e.g._ _Triprion_, _Diaglena_, _Amphodus_, and occasionally in _Pelobates_.

A few Anura possess peculiar substitutes for teeth in the anterior portion of the lower jaw, namely, a pair of conical bony processes, sometimes rather long, but always covered by the dense gums, or investment of the jaws; _e.g._ _Lepidobatrachus_, several Rana, _e.g._ _R. adspersa_, _R. khasiana_, _R. kuhli_, and _Cryptotis brevis_.

{31}Cranial dermal ossifications are developed in some species of _Bufo_, still more in the Hemiphractinae, and above all in _Pelobates cultripes_ and in the Cystignathoid genus _Calyptocephalus_.