Chapter V: Part 5

The first three teeth are usually larger than those which are placed behind them, in this respect rather resembling some fossil reptiles than Dolphins, and presenting a character like that seen in the Dimorphodon. They are placed in oblique oval sockets. They have a single fang like Cetaceans, Edentates, Reptiles, and like the premaxillary teeth of Mammals. Cambridge specimens of jaws are not sufficiently perfect to show whether the teeth are limited to the premaxillary bone; but this appears to be the case in _Pterodactylus crassirostris_ (Goldf.), and probably in _Ornithocheirus compressirostris_ (Owen), [_Palæontographical Society_, 1851, Pl. 27], and is so regarded by Professor Owen in his later writings. Yet the significance of this fact seems to have been forgotten, and Cuvier's dictum about their teeth still has influence. He says, "The teeth, by which the examination of an animal ought always to be commenced, here present nothing equivocal. They are all simple, conical, and nearly alike, as in the crocodiles, monitors, and other lizards." But, on the one hand, the Dolphins demonstrate that a mammal might have similar teeth even in the maxillary bone; and, on the other hand, since teeth in the premaxillary bone always are single-fanged, and commonly have a simple sub-conical crown, there is absolutely no evidence in the teeth of the affinities of the animal, which, so far as this portion of its economy went, might as well have been a fish or a mammal as anything else. In the succession there is nothing very distinctive. In the Crocodile one tooth comes up under another, as is commonly the case with mammals; and in mammals the fangs of the old teeth are often partially absorbed so that the teeth drop out into the mouth. In the Pterodactyle the new teeth came up on the inner side, as in the Ichthyosauria--a tribe of animals as singular in their affinities as the Ornithosauria. Occasionally specimens show a small furrow on the inner side of the fang, indicating absorption, but there is nothing to show how many times the teeth were renewed: in the Dolphins there is but one set, and in Crocodiles the teeth are replaced many times. In form and size the teeth are very variable. They are directed obliquely forward, and are curved backward and inward. They taper in an elongate cone, compressed from side to side, flattened on the outside, moderately convex on the inside; rarely the sides meet in a ridge after the plan of Pliosaurus, Megalosaurus, Dakosaurus, &c.; more frequently the lateral margins round into each other. Usually the enamel is quite smooth, sometimes, as in No. 1, it is finely striated and wrinkled. Some teeth are nearly circular and some quite straight. The ovate fang contracts below, conically, and is closed, leaving a long hollow pulp-cavity in its interior. Nos. 9, 10 show the marks of the successional teeth on their inner sides. No. 11 appears to have had the crown slightly worn at the tip during the animal's lifetime. In transverse section of the crown the tooth structure resembles Ichthyosaurus, Cetaceans, and Bats. The dentine is filled with calciferous tubes which radiate as in Ichthyosaurus, and towards the centre of the tooth are seen in transverse section to present many angles, almost like radiated corpuscles. They are separated by interspaces of their own width, and run towards the circumference, sometimes straight and sometimes wavy, parallel to each other. They send off branches usually at right angles which anastomose with the adjoining tubes. The dentine is in concentric layers, and shows layers of sub-circular cells as in the teeth of Mammals. The enamel is a thin transparent layer with fewer and finer tubes than the dentine.

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A SUMMING UP.

The story of the structure of the Ornithosaurians of the Cambridge Greensand has now been told, and it only remains to gather up the threads of their affinities and determine the Pterodactyle's place in nature. But before doing so, so various in importance are the characters enumerated, that I would first offer a few remarks on the classificational value of characters among the Reptilia, with which Pterodactyles have been most commonly grouped.

The naturalist who only examines organisms now living on the earth, symbolizes to himself, by the term Reptile, a definite sum of characters, with definite subdivisions and subordinate grouping, to which the extinct types of life extricated from the rocks cannot entirely be adapted. When the fragmentary, and often isolated or ill-associated, bones of fossilized animals are contrasted with corresponding bones in the skeletons of Serpents, Crocodiles, Lizards and Turtles, not infrequently it is found that the characters attributed to different Ordinal groups are interlaced in a single individual with a type of organization peculiar to itself, and important as are the modifications of existing orders. These characters occasionally are grouped with others which in living animals had been deemed characteristic of Fishes, Amphibia, Birds, and Mammals.

The Reptilia of the Palæontologist is therefore a vast and provisional group, ever acquiring new characters, to which no diagnosis can be applied. And although certain empirical characters have served to allocate the specimens in their several orders, in general with sufficient accuracy, yet from the imperfect preservation of some of the remains, or the imperfect extent to which their structures are known, and the want of recognised canons by which to measure their relative values, it has not been possible to discuss the relations of the several orders to each other or with the larger groups on which some of them impinge.

Classifications represent more or less faithfully the gradational increase in the sum of the characters of an organism, as well as the increase in importance that those character severally attain. Thus gathering, so far as may be, from the chaos of individuals, _a common plan of structures_ on which the genus, order, or class is moulded from a less specialized group of organs. The fundamental structures of a vertebrate animal, so far as their persistent importance can be measured, are, those connected with

I. Perpetuating the race.

II. Construction of the brain.

III. Circulation and oxidation of the blood.

IV. Locomotion, i.e. skeleton, muscles, &c.

And these characteristics are for the most part so interlinked, that it becomes difficult to assign to one order of animals a relative superiority over another order; since when a single set of organs is prominently developed in one group it often happens that another set of organs has a like pre-eminence in an allied group. Thus among reptiles it might be considered that

_Crocodiles_ have the best hearts, and _Turtles_ the best lungs.

And since these structures in their functions severally modify and determine the use of other structures, the meaning that terms like Crocodilian and Chelonian really have is that they represent the aspect of Reptilian organization when seen through the specialization of respiration, or circulation of the blood. The soft parts thus determining the nutrition and function of the muscles and skeleton, anatomists in examining the bones of extinct animals are accustomed to reverse the order of their inferences, and infer from modifications of the skeleton what had been the characters of the soft and more vital structures.

On the presumed accuracy of this method of research rest many results of Comparative Anatomy. But since the shapes of bones are determined by the muscles as well as by inheritance, it is always to be remembered that a similar form of bone may obtain in different orders or classes of animals, as the result of a similar function in a special region of the body. Such resemblances are familiar to anatomists. Hence much caution is required from the Palæontologist to distinguish between the characteristics of a group, and the extent to which they may be modified by function. This distinction is the first principle of classification. But it is always difficult to estimate the importance of characters in fragments of bones or parts of skeletons, and the difficulty is increased by the fact that if what appears to be but a functional modification should pervade all the species, it becomes a characteristic of the group, and its power of modifying the other organs in a peculiar way has to be considered.

Thus for all practical purposes birds may be said to be characterized by wings, which almost acquire the dignity of class characters from their influence on the respiratory function. But in some birds it has been thought that no bone of the fore-limb was ever developed[V]; and the difference between such a phenomenon and the wing of a Swift, for example, is one almost of infinity, as compared with any other aspect that the anterior limb might have assumed. Therefore, since a bird may part with its fore-limbs and yet remain a bird, I infer that it might apply its fore-limbs to the ground, become a quadruped, and be a bird still. And if in this process the other structures remained unchanged, no one would regard the modification as more than an ordinal one. But should the vertebræ change also, or the pelvis, or the covering of the integument, or the jaws become toothed, then, although the heart and lungs and brain of the imaginary animal retained their class characters, the functional differences being more than those of an order would constitute it a sub-class.

[Footnote V: According to Prof. Owen, in Dinornis.]

In the same way it is conceivable that serpents may have existed with well-developed limbs, and if they retained their other characters the limbed forms would constitute a sub-order of serpents; but if to these characters they added a closed palate united to the cranium, they would constitute a new order of reptiles. A chelonian might be entirely deprived of its bony covering, and it would still be a chelonian, differing only as a separate family. So that structures which to the eye appear fundamental may be lost without affecting an animal's systematic position, just as animals while resembling each other in form may possess dissimilar organization.

Even with the living or typical Reptilia, naturalists are divided as to the number of ordinal groups into which they naturally fall. It is however generally agreed that the Amphibia or Dipnoa of Fitzinger, have no near affinity with the true reptiles. Milne-Edwards, Van der Hoeven and Agassiz make the remainder into three orders, as did Cuvier:

Chelonia,
Sauria,
Ophidia.

Stannius, Gray, Owen and Huxley, on the other hand, by dividing the Saurians make four orders, to which Dr Günther by his description of Sphenodon has given evidence of a fifth:

Crocodilia,
Chelonia,
Sauria,
Ophidia,
(Rhynchocephalia.)

De Blainville in a remarkable classification (1816), made three orders, Chelonians, Emydosaurians [crocodiles], and Saurophidians; the latter group being subdivided into Saurians and Ophidians.

In his "Handbuch der Anatomie der Wirbelthiere" Stannius unites the Crocodilia and Chelonia into a group called Monimostylica; while of the Sauria and Ophidia he makes another group called Streptostylica. Similar groups were made by Dr Gray, and named Cataphracta and Squamata. They are identical with the "cuirassed" and "scaly" reptiles of Dumeril and Bibron.

The _Astylica_ (Sphenodon) have no penis.

The _Streptostylica_ have a double penis, lungs simplified at the distal end into a mere air-bladder, brains with a moderately elongated cerebrum, the palate mesially open, scales, leathery shell to the egg cut through by a tooth on the premaxillary bone.

The _Monimostylica_ have a single penis, lungs well subdivided, ventricle of heart partly [turtles] or entirely divided [crocodiles], brains having the cerebrum broad or high, a closed palate, scutes, a calcareous shell to the egg.

Thus the chief differences between Turtles and Crocodiles on the one hand, and Lizards and Serpents on the other hand, are not so much in the fundamental vital structures, though these undergo changes even in the families, as in the different ways in which the muscles and skeleton are modified. The typical lizards diverge widely from the crocodiles, and in those osteological features which admit of comparison they make at least as near an approach to the Chelonians. But leaving the limbs and pectoral and pelvic girdles out of consideration, lizards find their natural place side by side with the serpents.

Attempts have been made by Palæontologists to incorporate the new ordinal groups which they have been compelled to create for some fossils, along with the true Reptilia; but such a proceeding destroys the value of the term Reptile as a measure of a known organization. In the absence of knowledge of the brains of Dinosaurs, Ichthyosaurs, and Dicynodonts, their union with the Reptilia can only have a stagnating effect on Palæontology, for there is no proof that they are Reptiles in the same sense as are Crocodiles or Chameleons: while their bones being used as standards of Reptilian structure in comparisons, they adjudicate the place in nature of other animals by an authority which has never been established.

Before any inference can be drawn from the forms of bones in extinct animals, their relations to vital structures and to way of life must be known in animals which still live. This may give some clue both to their functional significance and to the extent to which they are inherited and not directly attributable to function. But an idea of the morphological value of the bones of living animals is only gained by comparing them with the remains of their extinct allies, tracing the now imitative structure back to its origin in a function which has ceased to be displayed.

Professor Owen in his "Comparative Anatomy of the Vertebrates" (1866) admits nine orders of Reptiles, five of which are extinct, some of the extinct orders being supposed to rank lower, while others are higher than the living types. They are arranged in this way,

* Pterosauria,
* Dinosauria,
Crocodilia,
Ophidia,
Lacertilia,
Chelonia
* Anomodontia,
* Sauropterygia,
* Ichthyopterygia.+

* Extinct.

+ Prof. Owen, _Comp. Anat._ Vol. I. p. 7-9, defines his
sub-classes. At p. 15, in the details of the orders, he puts
Ichthyosaurus in the 5th sub-class _Monopnoa_. But at p. 50,
treating of the vertebral column of Ichthyosaurus, it is written of
as an extinct order of _Dipnoal_ reptiles. The Dipnoa then
would include

Ichthyosauria,
Batrachia,
Labyrinthodontia,
Ganocephala.

But Ichthyosaurus obviously belongs to Haeckel's group Monocondylia.

In what characters the Ichthyosaurs are lower than living reptiles I have been unable to discover. The palate may be better compared with a struthious bird than with a reptile; and the pectoral girdle may be better compared with the Ornithodelphia than with a reptile, while all the trunk-vertebræ have ribs such as are associated in living animals with a four-celled heart. But if it is a lower animal type than living reptilia, the student will ask, how much lower? does it descend to the Dipnoa, and prove to be the missing link between the Amphibia and Reptilia? and wherein is the evidence? Or does it not with Dicynodonts and Dinosaurs rather form an outlying class uniting the reptiles with the mammals.

In the same way, when Pterosauria and Dinosauria are placed above living reptiles, we are compelled to ask how much are they above, or what are the characters which bind them to the Reptilia at all? No satisfactory evidence has ever been adduced to show that the Dinosauria are Reptiles. And of the claim of the Pterodactyles to such a position, the facts detailed and now summarised will be the best evidence.

The highest structure shown in these remains is the brain-case. The cavity for the brain is in every respect like that in the skull of a bird. It resembles brains of a high type in having the cerebral lobes convex in front; since, in the lower mammals, there is a resemblance to reptiles in the conical form of the cerebrum; while the brains even of some of the placental mammals are not well distinguished from those of reptiles. Although the brain of the Ornithorhynchus is entirely mammalian, it is more like the brain of a reptile than is the brain of the Pterodactyle. No evidence of affinities could be adduced which would outweigh this. Taken by itself it would lead us to anticipate for the Pterodactyle those vital structures which birds have in common.

Next in importance to the brain are the pneumatic perforations in the bones. They are seen in the lower jaw, the quadrate bone, in the whole of the vertebral column, in all the bones of the fore-limb, excepting one or two fragments, in the scapula and coracoid, in the os innominatum, in the femur and in the tibia. In such of the bones as can be compared, the pneumatic perforation is usually situated in Birds as it is in Pterodactyles. In Birds the bones are filled with air through these perforations, and as a principle the greater the motion of the animal, the greater is the number of bones filled with air. This air is received from the air-sacs which receive it from the lungs, and return it through the lungs again. There is thus in birds a sort of supplemental lung-system, which circulates air through the body. Nothing of the kind exists in any other class of animals. The respiratory system in birds is more perfect and complex than in the other vertebrata, and, as a result, the temperature of the blood on the whole is hotter.

In Pterodactyles the reticulate character of the perforations proves that they were pneumatic, and supplied the bones with air. The fact that the bones were supplied with air, necessitates an elaborate system of air-sacs to furnish the supply. And the existence of these air-sacs speaks incontestably to bronchial tubes opening on the surface of the lungs to supply them, and to the existence of lungs essentially like those of birds. The outward and backward direction of the coracoid bones may indicate that the lungs were larger than in a bird.

The circulation of air through the bird's body has relation to rapid motion through the atmosphere, which necessarily produces more rapid respiration than would comparative quiescence. The same inference must be applied to the Pterodactyles. But rapid respiration only means more rapid oxidation of the blood, and conversion of the purple cruorine into scarlet cruorine,--that is, the conversion of venous blood into arterial blood. And if venous blood is converted into arterial blood by a lung-apparatus like that of a bird, and with a rapidity like that in a bird, there must be a circulation of the blood as rapid as in birds. Such a circulation is only maintained by a heart with two auricles and two ventricles. Therefore Pterodactyles had the heart like that of birds and mammals.

Now, since the temperature of the blood is chiefly dependent on respiration and circulation, and Pterodactyles had respiratory and circulatory organs which in living animals produce hot blood, it results that they were hot-blooded animals.

Thus the heart and lungs are exactly such as would have been inferred from the brain, and, like it, they are avian. And so important are these vital structures all taken together, that the inference from them upon an animal's affinities would overbear all other evidence that could be adduced except reproduction; for they demonstrate the plan on which an animal was built, and are the motor power which enabled it to use its skeleton in a way that stamped upon it a peculiar form.

In the head such structures as are preserved conform with slight variations to the avian plan. Other Ornithosaurians show in the parts which are not preserved in Cambridge specimens some characters which are not avian; they are in part as much mammalian as reptilian, and in a few points entirely reptilian. But it might be misleading to take German specimens into consideration in forming an estimate of the Pterodactyles of the Cambridge Greensand, which were probably a different ordinal group, and may have had material differences in structure.

The vertebral column as a whole is distinctive.

The neck and sacrum are mammalian, and the tail reptilian. The procœlous vertebræ are characteristic of reptiles, but in some animals, as Chelonians, they vary in different regions of the body; and among amphibians the character is inconstant in genera nearly allied.

The hind-limb is in part mammalian and in part avian; if there be any reptilian characters in the foot, they are not less mammalian.

The os innominatum is avian and mammalian.

The pectoral girdle is avian.

The fore-limb is avian and mammalian.

The wing-finger is distinctive, though formed on the avian plan.

Thus, if with an avian basis some parts of the skeleton present points of agreement with reptiles, in other points there are resemblances with mammals not less characteristic. These phænomena do not show that in so far the animal is a mammal or a reptile, but only that mammals, ornithosaurians, and reptiles have had a common origin, and that while they have been differentiated so as to form separate classes they have severally retained characters which formerly were united in one class. It is a skeleton intermediate between reptiles and mammals, and well distinguished by mammalian, reptilian, and peculiar characters, from birds. It therefore forms a parallel group with birds, displaying the ornithic organization in a differently modified skeleton. Yet it differs more from existing birds than they differ among themselves, for the discrepancies are in points of structure in which all existing birds agree: they are in having teeth, in the procœlous centrum, in the separate condition of the carpal and metacarpal (and of the tarsal and metatarsal) bones; in having more than two bones in the fore-arm, in the sacrum formed of few vertebræ, in the expanded pubic (and prepubic) bones, in a long neck to the femur, and in the modification of the wing by the great development of the phalanges of one finger.

I therefore regard the Pterodactyles as forming a group of equal value with birds, for which group the name Ornithosauria is here used. It cannot form a separate class, because they have a fundamental organization in common; and it cannot form an order of birds, because its differences from birds are greater than those of an order. It is a group which itself probably includes several orders, and must constitute a sub-class, which finds its place in nature side by side with birds and between mammals and reptiles, thus:--

Mammalia. \
|
| Ornithosauria. Aves
|
Reptilia. /

Restoration.

Of the form and size[W] of the animals from the Cambridge Greensand, an idea will best be given by a few measurements.

[Footnote W: There are Ornithosaurians hereafter to be described compared with which the largest at present known will seem diminutive. A vertebra of one such, from the Wealden, is contained in the British Museum (numbered 28632). The centrum alone is between 9 and 10 inches long and 8 inches deep. It is named Streptospondylus, but constitutes a new group of Ornithosaurians. Nothing so gigantic exists in the Woodwardian Museum. Another vertebra of the same or an allied genus has been figured by Prof. Owen as the tympanic bone of ?Iguonodon (Fossil Reptilia of the Wealden, Part 2, pl. 10).]

In the species Ornithocheirus nasutus (Seeley), =J=._c_.2.11.1:

The premaxillary extends for 6 inches without reaching the nares.

The lower jaw is 3/4 of an inch deep at the articulation.

The four cervical vertebræ are each 1-1/2 inch long.

The sternum measures 1-1/2 inch over the facets for the coracoids.

The humerus is 2-1/16 inches over the proximal end, the radial crest not being preserved.

The coracoid is 1-1/4 inch over the proximal end.

The scapula is about 3-1/2 inches long.

The proximal carpal (imperfect) is 1-5/8 inch wide.

The distal carpal is 1-1/2 inch wide.

The lateral carpal is 1-1/4 inch long.

The wing-metacarpal is 1-1/4 inch wide at the proximal end, and 7/8 inch wide at the distal end.

The proximal end of the first phalange is about 1-5/8 inch wide.

The proximal end of the second phalange is less than an inch wide.

The claw-phalange (imperfect) is about 1-1/4 inch long.

The femur is 4 inches long.

Putting the animal together, the bones give this size :

Head 1 ft. 3 in. long.
Neck 9 "
(_Back and sacrum_) ? 8 "
(_Tail_) ? 10 "

With the hypothetical parts, this would give a length of about 3 ft. 6 in. from the tip of the snout to the tip of the tail. Then

Humerus 8 in. long.
(_Fore-arm_) ?1 ft. 0 "
Carpus 2 "
Metacarpus 10 "

Which, if the fore-limbs were kept together as in ordinary quadrupeds, would give a height to the body of about 2 ft. 6 in., but as the limbs probably spread in walking as among the bats, the hind-limb would give a better idea of the height of the animal.

(Flesh, sacrum, os innominatum). 2 in.
Femur 4 "
(_Tibia_) 6 "
(Metatarsus, &c.) 1 "

Which would give a height of about 13 inches; and, standing in the position of a bird, the height to the crown of the head would be about 2 feet. The majority of the Ornithosaurians of the Cambridge Greensand are of this size.

The spread of the wings, if there were 4 phalanges, would be

Body 10 in. wide.
Two arms 5 ft. 2 "
Two wing fingers 7 0 "

Giving a total expanse of about 13 feet. But, from the indications of the wing-finger, I should incline to think an expanse of 10 feet a truer estimate. The largest species attained to twice this size, and the smallest was a fourth as large. Another memoir will present descriptions and restorations of the Greensand species.

Habits.

The varying organization of different Ornithosaurians probably depends on the different habits of the tribes. That they could all fly is probable from the enormous radial crest to the humerus and the great development of the wing-bones, to which a wing-membrane was stretched, comparable to that of a Bat in texture, but more comparable to a Bird in its extent. The groups with long hind-legs probably had the membrane limited to the bones of the arm, while in the species with small hind-legs it may have attained even as great a development as in Bats, though there is no reason for suspecting that it extended to the tail. A Pterodactyle cannot be supposed to have hung itself up by the hind-legs as does a Bat, because the hind-claws appear invariably to be directed forward. A Bat walks upon four legs with considerable elegance and speed; the wing is folded in, close to the side, so as to be scarcely noticed; and the outer claw is free to climb with. There can be little doubt but that Pterodactyles walked in a similar way. The thickened mammilate knob at the proximal end of the first phalange is well calculated for contact with the ground. And if it were supposed that the large wing-metacarpal bone were only used to support the wing, and the small metacarpals only used to support the claws by which the creature has sometimes been pictured suspending itself, it would be difficult to believe that the forces of pressure and tension in flying so exactly corresponded to the forces manifested in suspension as to cause the large and the small metacarpals invariably to attain the same length. A correspondence of this kind may be presumed to indicate a correspondence in function; and since the animal did not fly by means of its claws, the inference is that it walked by means of the metacarpal bones. In no other way could the bones have been used equally. The avian ilium would suggest a probability that they also at times stood erect like birds, from which position they could with more ease expand their wings; nor is such an idea opposed by the resemblance of some bones of the hind-limb to what obtains in birds, and of the neck of the femur to what is seen in mammals of great power in the hind-legs.

That they lived exclusively upon land and in air is improbable, considering the circumstances under which their remains are found. It is likely that they haunted the sea-shores, and, while sometimes rowing themselves over the water with their powerful wings, used the wing-membrane as does the Bat to enclose their prey and bring it to the mouth. But the superior development of the pneumatic foramina suggest that their activity was greater than in ordinary sea-birds.

The large Cambridge Pterodactyles probably pursued a more substantial prey than dragon-flies. Their teeth are well suited for fish, but probably fowl and small mammal, and even fruits, made a variety in their food. As the lord of the cliff, it may be presumed to have taken toll of all animals that could be conquered with tooth and nail. From its brain it might be regarded as an intelligent animal. The jaws present indications of having been sheathed with a horny covering, and some of the species show a rugose anterior termination of the snout suggestive of fleshy lips like those of the Bat, and which may have been similarly used to stretch and clean the wing-membrane.

The high temperature, coupled with the sub-aerial life, are opposed to the idea of the animal having been naked. The undisturbed condition of the skeleton and some points of structure are opposed to the idea of their having had large feathers. The absence of such remains does not favour the hypothesis of their having been covered with scales, though in the legs of birds a scaly covering is met with. I should anticipate for them a filamentous downy feather, or hair, like a Bat's. The Bat combs its hair with its claws, and the Ornithosaurians may have used their claws in a similar way.

They cannot be supposed to have been gregarious, from the large number of species relatively to specimens. The reproduction may have been much the same as in birds; and the young were probably reared with affectionate care[X].

[Footnote X: Mr Carruthers has shown me crushed Turtle-like eggs from the Stonesfield slate, which in the external pitting of the egg-shell are not so different from some birds as to preclude a suspicion that they might possibly be Ornithosaurian.]

* * * * *

_The following notes indicate structures in perfect specimens from the Lithographic slate which supplement the fragmentary remains from the Cambridge Greensand_[Y].

[Footnote Y: The German animals form different family groups. And it cannot be inferred that the structures seen in them pertained to Cambridge specimens.]

In the head, Cambridge specimens show no trace of the parts which are between the brain-cavity and the fore-part of the jaw. The form and condition of the orbits, nares, and of the space between them, vary in German specimens. Some Birds and certain Ruminants, such as deer, the giraffe, &c., have an interspace between the orbits and nares corresponding to that in some Pterodactyles, but no such perforation is found in living reptiles. In mammals it appears to be surrounded by the frontal, nasal, lachrymal, and often by the maxillary bone. In birds the bones appear to be the lachrymal, nasal, maxillary and premaxillary, as is the case with Pterodactyles, except that the nasal bones would seem sometimes to be excluded. The chief peculiarity of the Pterodactyle skull in this region is made by the malar bone (and, according to some authors, the maxillary also) sending up a process to meet the lachrymal. This is not seen in birds, but is characteristic of many mammals and reptiles.

The premaxillary bone is single, as in birds and Iguana; but it appears to attain as great a development as in birds, and to occupy the portion of the jaw which among reptiles and mammals is made by the maxillary bone. Owing to the great development of the premaxillary bones, the exterior nares are placed far back toward the middle of the skull as in birds, and not near the tip of the snout as in living reptiles and most mammals.

The orbits in Pterodactyles are surrounded with bone, as is commonly the case with mammals and reptiles. Among birds a complete orbit is seen among the parrots, in which it is completed below by a prolongation of the outer posterior corner of the frontal, which would correspond to the post-frontal bone, and by the lachrymal bone. Thus the malar bone, which in most mammals and reptiles forms an important part of the lower margin of the orbit, is in birds entirely excluded. In Pterodactyles the malar bone is placed between the lachrymal and the post-frontal process of the frontal bone.

The quadrate bone in German Pterodactyles, instead of being vertical as in birds, stretches obliquely forward below the malar bone, so that the articulation for the lower jaw is brought forward to be under the middle of the orbit. In _Pterodactylus Kochi_ and in other species there appears to be a process, or small separate triradiate bone, comparable to a diminished lacertian post-frontal, and homologous with the post-frontal process of the parrots. Its upper branch meets the frontal. In some genera the front appears to meet the malar. The lower branch goes to the front of the quadrate bone, and the backward branch goes to the squamosal immediately above the articulation for the quadrate bone. Thus it is a post-frontal bone resembling that of the Iguana, but modified and adapted to a cranium like that of a bird. Its form and size in the different genera are very variable. No similar development is seen among mammals, where the post-frontals have probably ceased to exist. It is a carious point of resemblance, but from the other resemblances to Iguana being so few it is robbed of much of its force as a mark of affinity, and becomes of interest chiefly as an evidence of independent persistence of structures.

The pterygoid and palatine bones approximate to those of bird and lizard in Pterodactylus crassirostris. And the bones in Pterodactylus suevicus, which Quenstedt names vomera, should rather have been named palatines. There is a bone in Goldfuss' specimen, between the malar and palatine, which he identifies with the transverse bone, but it is not seen in any other specimen.

The ribs sometimes appear to articulate by single heads, but in P. crassirostris they are apparently articulated as in the Crocodile. Some species show abdominal ribs like those of some reptiles; but the segments of the mammalian sternum and abdominal ribs are to be regarded as homologous structures. The vertebræ offer considerable variety in size and shape, but the greatest variation in number is seen in the tail, which is sometimes stiff and long, and sometimes short. The pelvic bones show a large amount of variation in different genera, often appearing to be crocodilian, sometimes lacertian, sometimes mammalian. In the aim the humerus is variable in the length of the radial crest, and the metacarpus also varies in length.

When the external similarity of the skeletons of birds is borne in mind, it is impossible, without disregard of classification altogether, to place animals differing so widely as do the different Ornithosaurians in the few genera in which they are at present packed.

CLASSIFICATION.

The orders of Ornithosaurians may be established hereafter. Under the name Pterosauria, Prof. Owen founded one order which has for its type the Pterodactylus longirostris.

Von Meyer proposed to separate this order into two groups, one with two phalanges in the wing-finger, of which Ornithopterus is the only example, forming his Diathri; while the other group, Tetrathri, or those "with four fingers, comprised all other Pterosaurians. The Tetrathri he again subdivided, following out, as he states, the suggestion of Munster and Goldfuss, into _Dentirostres_ or such Pterodactyles as have the jaws furnished with teeth to their anterior termination; and the _Subulirostres_, or such as want teeth at the extremities of the jaws. To the former group he left the name Pterodactylus, and to the latter was given the name Rhamphorhynchus. Von Meyer says that he might easily have made a few more species, as will be evident to those who inspect his plates, but he "believes that the students of living animals go too far in their tendency to subdivide:" a fancy that, if indulged in by Palæontologists, would have the effect of restoring the old Linnæan groups; and a complaint which, although often heard, has usually come from those who do not readily discern and appraise classificational characters. In Palæontology genera are sometimes co-extensive with orders, while species often mean genera. It may be wearisome to the collector to be lured on to follow the devious ways of a science, but Palæontology, the source whence the mysteries of existing nature must unravel their meaning, is the handmaid of all nature's truths which have been buried in evolving the existing creation; and a duty devolves upon Palæontologists to make the past an inseparable part of the present, by applying to the two the same scientific method.

A year previous to the formation of Owen's Pterosauria, Bonaparte named the Order Ornithosaurii, and divided it into a family--Pterodactylæ, and a sub-family Pterodactylinæ.

Fitzinger (_Systema Reptilium_, 1843) also used the same ordinal name, and recognized three genera--

_Pachyrhamphus_, of which the type is Pterodactylus crassirostris (Gold.).

_Pterodactylus_, with the type P. longirostris (Cuv.).

And _Ornithocephalus_, with the type O. brevirostris (Sömm.).

These and other attempts at classification all endeavour to subdivide Ornithosaurians by the head or by the tail. Other characters for primary divisions may be obtained from the pelvis.

In the majority of German Pterodactyles the ilium extends for a long distance in front of the os pubis, and only for a very short distance behind the large ischium; and the small pubis from its anterior margin gives attachment to a large prepubic bone, which resembles in form the os pubis of the Crocodile[Z], and is unlike that of the Monotreme. These appear to include the long-legged animals with short tails, at present called Pterodactyles, and form a well-marked family or order.

[Footnote Z: Prof. Haughton, from a study of the bones and muscles, came to the conclusion that the pubic bones of Crocodiles are the marsupial bones.]

Another kind of pelvis is that in which the ilium extends a short way in front of the acetabulum, in which the pelvic bones inclose a much larger space. These include the Cambridge Ornithosaurians, the Rhamphorhynchus, and the Dimorphodon, and form another well-marked family.

These long-tailed Pterodactyles subdivide into three sub-families--Rhamphorhynchæ, Dimorphodontæ, and Ornithocheiræ. The four families may then be defined thus:

_Pterodactylæ_. Tail short. Hind-legs long. Ilium narrow, extending
far anterior to the acetabulum; ischium extending behind the
acetabulum. Epipubic bones ficiform. Head with the middle holes
large, often confluent with the exterior nares. Jaws toothed to the
anterior extremity.

_Rhamphorhynchæ_. Tail long and stiff. Hind-legs short. Pubis and
ischium small, oblique to ilium, which extends less far anteriorly
than in Pterodactylæ. Epipubic bones narrow and bent; they unite
mesially and form a three-sided bow in front of the pelvis. Head
with the middle holes and nares both small. Jaws never toothed to
the anterior extremity.

_Dimorphodontæ_. Tail long and stiff. Hind-legs long. Pubis and
ischium forming an expanded sheet of bone at right angles with the
narrow ilium, which extends as far behind as in front [prepubic
bones triangular (?) attached by the apex of the triangle]. Head
with the nares and middle holes large. Quadrate bone large. Jaws
with large teeth at the extremities, and small teeth behind. No
sacrum.

_Ornithocheiræ_. Tail long and flexible. Hind-legs short. Pelvis as
in Dimorphodontæ. [Epipubic bones with a small attachment, form
unknown.] Head with the quadrate bone small. Sacrum of not fewer
than three vertebræ.

In the Pterodactylæ the genera are--

_Pterodactylus_ (Cuvier), in which the exterior nares are at the
sides of the face, very large, and only partially, if at all,
separated by bone from the small middle hole of the head. The head
is elongated. The neck is long. Among others, it includes the
species P. longirostris, P. Kochi, P. scolopaciceps, P. longicollum.

_Ornithocephalus_ (Sömmerring), in which the anterior nares are
entirely separated from the middle holes of the head, both being
small, and the latter exceedingly small. The head is short The
neck is short. The large ischium appears to be excluded from the
acetabulum, and the ilium appears to extend less far forward than
in Pterodactylus[AA].

[Footnote AA: So far as can be judged from figures, it appears to have but three bones in the wing-finger: what Cuvier regarded as a terminal and fourth joint, the bone _n_, Pl. XXIII. fig. 7, _Oss. Foss._, appearing to me to be the fibula of the tibia marked _e_. _s_ in the same figure would be the terminal phalange, and _r_ the first phalange, as may be proved by measuring them with those of the other hand, so that a phalange is missing from between them. Both the terminal phalanges appear to be hooked at the termination. Goldfuss figures the phalanges so as to make the bone which appears to be fibula in Sömmerring and Cuvier look like a fourth phalange.]

_Pachyrhamphus_ (Fitzinger). The nares are entirely separated from
the middle holes of the head; both are large. The head is thick
and massive. The prepubic bones meet mesially. No evidence of
the number of phalanges in the wing-finger. The quadrate bone
is massive, but has small attachment to the skull. Two sacral
vertebræ. Wing-metacarpal very short. The type is P. crassirostris
(Goldfuss).

_Cycnorhamphus_ (Seeley). Nares very small, looking upward from
a swan-like beak. The middle hole of the skull very large and
elongated and lateral. Neck long. Wing-metacarpal long. Four joints
in the wing-finger. Ilium widening in front. Epipubic bones meeting
mesially. The type is Pterodactylus suevicus (Quenstedt).

In the Rhamphorhynchæ at present there appears to be but one genus known:

Rhamphorhynchus (von Meyer). The nares and middle holes are both
small, ovate, of nearly equal size, and close together at the side
of the head in front of the orbit.

In the Dimorphodontæ the only genus is

_Dimorphodon_ (Owen). It has the nares enormously large. The middle
holes are also large.

In the Ornithocheiræ the genus is

_Ornithocheirus_ (Seeley), in which teeth are prolonged anterior to
the muzzle, and the palate has a longitudinal ridge.

With the osteological illustrations of the Ornithosauria are arranged some premaxillary bones, which show varieties of form of the snout. These variations of shape serve easily to indicate different species. And the following memoranda from those specimens and other specimens in the drawers form a synopsis of the species of the Cambridge genera, which may hereafter be fully elucidated from the copious materials in the series of associated remains.

I.

Ornithocheirus Sedgwicki (Owen).

Case. Comp. Tablet. Specimen.
=J= _c_ 13 2

The fragment is 2-7/8ths inches long, with the elliptical teeth opposite to each other, 6 on a side on the palate, and one pair in front. The first three teeth are large; behind these the teeth are about half the size. The palate is gently convex, with a faint median ridge, and measures from side to side over the fourth and subsequent sockets 13/16ths of an inch. The height of the jaw at the fourth socket 1-1/4 inch. The sides converge to an acute rounded rostral keel. The jaws appear to have been long. The anterior termination is vascular.

The rostral keel figured by Owen Pl. I, fig. 1 _d_, in the 1st Supt. _Cret. Reptiles_, is not square as represented there, but rounded; the sides converge more acutely, and at the ridge the keel is not half so wide as the figure makes it. The enormous size of the third tooth-socket is partly due to the cracked bone having absorbed more phosphate of lime than it could hold, and extended the cracks to fissures. The type specimen shows that there was another pair of sockets in front of, but quite close to, those which appear to terminate the lower jaw.

II.

Ornithocheirus Cuvieri (Bowerbank).

Case. Comp. Tablet. Specimen.
=J= _c_ 15 1-3

A portion of a premaxillary bone fractured at both ends, and two inches long, corresponds with Dr Bowerbank's fossil figured Pl. XXVII. fig. 1, 3, 4, in the Palæontographical volume for 1851. The palate is just as wide; the median ridge, the same; the teeth the same in shape and as far apart. The jaw is of the same depth, but does not deepen so rapidly behind. The only other difference is that the sockets of the teeth are less prominent on the sides, and appear to look more directly down.

The ridge in which the converging sides meet is well rounded in a dentary bone which may have pertained to this species. In the space of two inches and a quarter are 5 teeth, the posterior four extending over two inches, the other pair being in front. The palatal surface is 3/4 of an inch broad behind the third tooth, and rather more than 5/8 of an inch broad behind the fourth tooth. The length of the 4th or of the 5th sockets is two-thirds that of the second or third. In front of the 5th tooth, the jaw is an inch deep, and it tapers in a curve to the anterior end. The teeth behind the third have interspaces greater than the length of the sockets; that between the 4th and 5th being 3/8 of an inch, while the socket only measures a quarter of an inch long. Behind the 2nd socket commences the palatal groove, broad in fronts but narrowing behind; and its sides instead of diverging as in the type, are concave so as to form a channel like a straightened _Siliquaria_ shell. The halves of the palate bevel off so as to make a right angle with each other, and greater angles with the flat sides.

III.

Ornithocheirus machærorhynchus (Seeley).

Case. Comp. Tablet. Specimen.
=J= _c6_ 35 1

Dentary bone. Broken at both ends, and wanting all its teeth, this interesting fossil shows the suture where its whole length rests on the angular bone which almost reached to the termination of the beak, quite unlike what is seen in any German Pterodactyle.

It is a narrow mandible, less than three quarters of an inch wide, with the alveolar margins parallel. The palatal surface 1-1/2 inch long, is divided into 3 equal strips; the middle one being a deep glossal groove, slightly narrowing in front, and deepening behind, made by two inclined flat surfaces. The lateral strips are horizontal behind, and in front slope a little outward. The tooth-sockets are oval, directed outward, and as long as the interspaces, though these seem to get longer behind. In an inch and a quarter there are four teeth. Below the teeth, the sides of the jaw are compressed: though nearly parallel at the hinder fracture, the flattened surfaces approximate in front till they meet in a sharp keel, which appears to make an acute angle of about 45° with the palate; and below, where the jaw is an inch deep extends for half an inch in front of the suture with the angular bone: this suture is straight and irregularly concave, and in an inch and a quarter approximates to within 5/8ths of an inch of the palate.

IV.

Ornithocheirus tenuirostris (Seeley).

Case. Comp. Tablet. Specimen.
=J= _c2_ 12 1

Middle part of a premaxillary bone fractured behind and in front, slightly distorted by compression; it is 2-1/8th inches long, and nearly resembles _O. compressirostris_ (Owen). The palate is about 1/2 an inch wide in front, and 5/8ths of an inch wide behind; it is compressed mesially into a strong angular keel, between which and the teeth there is a shallow groove on each side. The groove dies away behind, and the converging parts of the keel occupy the whole space between the teeth. The teeth-sockets are small, elliptical, not opposite to each other, and placed along a distinct flattened tooth area, which looks downward and outward and separates the palate from the side of the jaw. The first pair of sockets preserved are almost 3/16ths of an inch long and 1/16th of an inch wide. The interspace between that tooth and the next tooth behind is 7/16 of an inch. Separated by similar interspaces, behind these on one side are two sockets, and on the other side one socket. The sides are flattened in front, and convex behind, (making the section of the jaw lanceolate); they are compressed and round into a narrow rostral keel. The height from the palatal ridge to the rostral keel in front is 11/16ths of an inch; behind it is fractured, but the height was probably 14/16ths of an inch.

The palatal keel, distance of the teeth, and proportions of the jaw, distinguish it from O. compressirostris (Owen).

V.

Ornithocheirus Oweni (Seeley).

Case. Comp. Tablet.
=J= _c_ 20

The small piece of premaxillary on which this species is founded indicates a small animal, and nearly resembles the jaw of _O. microdon_.

It is scarcely an inch long; nearly 9/16ths inch high behind, and nearly 7/16ths of an inch high in front, so that it tapers very rapidly, and could scarcely have been an inch longer in front.

The nose is well rounded, but the sides are a little concave, and become well pinched in in the middle, behind, showing the near approach as I think to the nostril.

The palate half an inch broad, is divided into two concave channels by the strong and sharp median ridge, which projects below the alveolar margins. The dental margins are not rounded as in _C. microdon_, but flattened, making more than a right angle with both the outer side-wall and palate. The interspaces between the teeth are rough, looking as though they had supported minute teeth. The alveolar margin is a tenth of an inch wide; along it are the perfectly circular sockets, a sixteenth of an inch in diameter. There are 3 sockets between 5/8 of an inch, so that they are separated by 3 times their diameter. The palate is obliquely impressed with blood-vessels running forward to the teeth from the median ridge.

The points in which this jaw differs from that of _O. microdon_ are that in this species the teeth are circular instead of being oval; that the interspaces here are as long as in that species, though this jaw is only two-thirds the width; that instead of having a sharp keel on the upper surface, this has a well rounded roof. That though the jaw is scarcely higher than it is wide, it shows strong furrows running up to the nares, while in _O. microdon_, though the proportions are the same, the sides are perfectly flat without trace of pinching in, while the line of the nasal opening is indicated by a faint furrow running all along the jaw. And lastly it differs in size, which, where the sutures are lost, may be important in discriminating forms.

VI.

Ornithocheirus microdon (Seeley).

Case. Comp. Tablet. Specimen.
=J= _c_ 29 1-2

Premaxillary bone. The fossil is nearly 1-3/4ths inch long, and at the proximal end, where it is less than 3/4ths of an inch high, has flat sides, which converge to form a keel which is depressed anteriorly and rounded so that where fractured in front the bone is 7/16ths of an inch deep. The palatal surface contains two wide concave channels, between which descends a sharp median ridge, which behind becomes more prominent than the alveolar border.

The palate is 5/8ths of an inch wide. The alveolar margins are compressed and rounded. The small tooth-sockets are oval, and four are contained in 1-1/8th inch; they look downward.

There is a small tip of a jaw associated with this fossil, which is so like that it might be part of the bone broken off before fossilization. It corresponds in every way except that the teeth are closer. In this terminal lanceolate fragment there are in 5/8ths of an inch four teeth. The snout is terminated by two, which are close together.

VII.

Ornithocheirus Huxleyi (Seeley).

The only specimen of this species yet known is the greater part of a dentary bone contained in the Museum of the Geological Survey. An inch and 1/4 long and 3/4ths of an inch wide, it is less than half an inch deep: the sides slowly converge towards the front, and it appears to have had an obtusely lanceolate beak. The under surface is convex, too inflated for trace of a keel, and tapers to the end of the beak, which, with the left alveolar margin is abraded. The palatal surface is smooth at its front end, but two diverging ridges soon arise and form the boundary of a posteriorly deepening mesial channel, which is a quarter of an inch wide at the fracture. These ridges too, which are parallel with the compressed and rounded alveolar margins, convert the lateral spaces into shallow channels. The right side shows the sockets of 3 small oval teeth separated by interspaces wider than teeth. A tooth and two interspaces measure 7/16ths of an inch.

The only cretaceous Pterodactyle which this at all resembles is _O. microdon_, but the palate is wider than in that species; the sides converge towards each other more rapidly, as though it belonged to a species with a shorter snout.

I am indebted to Prof. Huxley for the opportunity of making a notice of this species.

VIII.

Ornithocheirus oxyrhinus (Seeley).

Case. Comp. Tablet. Specimen.
=J= _c2_ 13 1