Chapter II: Part 2

In certain Pterodactyles the proximal condyle of the femur resembles birds; but in other Pterodactyles the bone is more mammal-like in its straightness, and development of the upper condyle, and in the presence of a trochanter.

_The tibia and fibula_

may be compared, from their great length, with birds and flying vertebrate animals.

The fibula is style-shaped, like that of a bird, the lower part being wanting; while in bats the upper part is wanting.

_The tarsus,_

of two rows, is best compared with that of reptiles. The number of constituent bones has not been definitely determined.

_The metatarsus_

shows a certain return from the bird type to that of reptiles.

_Foot._

Von Meyer never finds more than four toes, and sometimes a stump of a fifth. As a whole, the foot is Saurian-like. It differs from lizards in the number of toes, and approximates to Crocodiles. In Pterodactylus longirostris the formula of the toes is 2, 3, 4, 5, with a stump of two joints;--like lizards, if we abstract the outer toe; and like birds with four toes; but they are liable to variations.

In Pterodactylus scolopaciceps and P. Kochi the formula is 2, 3, 3, 4 joints. In Winkler's specimen of P. Kochi there is also a stump of three joints.

In Pterodactylus micronyx the formula is 2, 3, 3, 3, and a stump of two joints. In P. longicollum the number appears to be different from all the foregoing.

The stump was attached to the side of the outer toe. Wagner, in P. Kochi, supposed it to be on the inner side, and so gave a reverse arrangement to the toes. The stump may be compared with that of some Chelonians, in which it is not furnished with a claw.

There is a difference from birds in the claws being much less developed. It has a true reptile foot. In bats the toes are of equal length. Von Meyer thinks the hind-legs did not enable it to walk on the land.

In some Pterodactyles the flying-membrane is faintly seen. The presence of feathers might be inferred from there being but one finger for flighty as in birds; but the function of feathers is subserved by the long and stiff finger. If it had been covered with scales, as was supposed by Cuvier, some traces of them would be found. The skin was probably naked, and had no connection with the hind-legs as it has in bats; in this respect resembling birds.

The condition of the several parts of the skeleton completely proves that the Pterodactyle was a reptile. Its head, neck, shoulder, and back, resemble a bird; while there are, on the other hand, some striking resemblances with the reptile in the pelvis, tail, and articular parts of the limbs. Sometimes the characters of the two classes run side by side, as in the skull, the fore-limbs, and especially in the hind-limbs, where the shin of a Bird is connected with the foot of a Saurian. The parts in which it corresponds with birds show that Pterodactyles also were flying animals. That we should be entitled to conclude, from the hollow state of the bones, that they belonged to flying animals, is sufficiently proved by Blumenbach, Buckland, Mantell, Owen having mistaken them for bones of birds.

The most absolute proof that it was a flying animal is the pneumatic character of its bones. This condition was discerned by me in some Pterodactyle bones from the Lias of Franken (_Jahrb. für Mineral_, 1837, p. 316), and was afterwards established by Owen in the Pterodactyles from the Chalk of England. This structure was previously only known in birds. And the supposition readily follows that in the respiratory process there was some similarity between the Pterodactyle and the Birds. They have the proportions of upper-arm and fore-arm which characterize birds of great flight, the humerus short and the fore-arm long; hence it may be presumed that Pterodactyles could fly well. From the absence and presence of the bony sclerotic ring in the eye, it may be supposed that the Pterodactyles were active in the day-time, while Rhamphorhynchus was nocturnal.

After this statement von Meyer gives a discursive summary, in which his views of the classification of reptiles in general and of Pterodactyles in particular are epitomized. And then goes on to combat the views of people who have departed from his classification and attempted to set up classifications of their own; and cites a number of authors who, labouring at the vertebrata, have endeavoured to find a resting-place in their systems for the Pterodactyle. But the chief thing we learn of von Meyer's own views is, that in 1830 he published a classification of extinct Saurians, dividing them into those with limbs like the larger and heavier land-mammals, those with fin-like limbs, and those with a flying-finger. Which divisions have been widely adopted, though authors have sometimes given them other names than those by which they were first made known.

Von Meyer has freely stated the facts about the Pterodactyle, and draws the conclusion that the animal was a reptile; but how such a conclusion was obtained from such facts is a matter on which his pages are silent. One seems to hear the chirrup of the bird in almost every paragraph. The head is in the main a bird's head; the pectoral girdle and the sternal ribs are those of a bird; and very few are the structures in which some reminder of the bird is not present; and in their bones he discovered the pneumatic characteristic and inferred, for the animals bird-like lungs. How, then, comes it that the Pterodactyle is a reptile? We can only suppose the answer to be, Because if the head and pectoral girdle and other bones had been reptilian it would have been a bird.

* * * * *

In the views here epitomized it is difficult always to make out the logical foundations of the conclusions arrived at. Sometimes they have no foundations, and sometimes they represent the different aspects in which a truth presents itself to minds differently constituted or differently conversant with the structures of living animals. In now stating my own views I shall avail myself of the example of some previous writers, and attempt to investigate the Pterodactyle as though they had not written. And then, having placed before him all the theories that are known, the reader will be able to choose the theory that pleases him best, if indeed he needs one.

Much of the discrepancy of opinion that exists is probably due to the use of the inductive method of thought for the discovery of fundamental principles in classification. In palæontology, where the types are more generalized than are living forms, it must always be difficult to reason from the known to the unknown. The known is always more or less incomparable with the unknown; and there can be no reason for inferring that the specialities of structure which now accompany specialities in organization would justify us in inferring for the animal, in which the structures formerly were united, the combined organizations of the living animals in which they are now found. On any hypothesis of evolution it would be allowed that the special modifications of a group were attained subsequently to the common plan of the larger group to which it belongs, and are entirely to be attributed to the function which the necessities or organization of the animal caused its structures to subserve. Inductive thought may sometimes discover function from structure, but never makes more than an approximate guess when it endeavours to determine fundamental organization from osseous structures which are not fundamental. And before a naturalist can say, since an animal has for instance a tail like a mammal that in so far it must be affiliated to the mammalia, he must have determined why the mammalian tail has its peculiar characters, and whether it is compatible with any other common plan of organization. And perhaps it might with equal reason be considered reptilian.

Therefore I prefer at firsts instead of reasoning from the details of structure, to adopt the _à priori_ method, and ask, not what the Pterodactyle is like in its several bones, but what common plan it had whereon its hard structures were necessarily moulded. For I imagine, if it can be determined what the nervous and respiratory and circulatory structures of the Pterodactyle were, it becomes a secondary matter to know whether the phalanges are like a lizard's, or the pelvis like that of a mammal. If the animal is asserted to be a mammal, a reptile, or a bird, we ought to be able to adduce evidence that it had the soft parts which are deemed distinctive of the selected class. This no one has done or attempted to do.

Hereafter it will be necessary to describe the Pterodactyle's brain.

There is no organ more distinctive between hot-blooded animals on the one hand, and cold-blooded animals on the other, than the brain. In the cold-blooded groups, or those in which respiration is feeble and circulation imperfect, that is to say, in existing fishes, amphibians, and reptiles, the parts of the brain are arranged one behind another, so that when looked upon from above, a portion called the optic lobes intervenes between the anterior masses called the cerebrum and the posterior mass called the cerebellum. In the hot-blooded groups, or those with an enormous extent of lung-surface for oxidation of the blood and a four-celled heart for its rapid circulation, that is to say, in birds and mammals, the front part of the brain called the cerebrum is immensely developed in proportion to the other parts, and abuts against the cerebellum and more or less completely covers the optic lobes, which in birds are squeezed out to the sides. The Pterodactyle brain is of this latter kind. And it being taken as a postulate that this kind of brain is the product of the organization which produces hot blood, it follows that the Pterodactyle was a hot-blooded animal.

Again, the Pterodactyle has perforations for pneumatic cells in many of the bones.

There is no structure in the animal kingdom more distinctive of a Class of animals than air-cells perforating the limb-bones. They are connected with a peculiar kind of lung and heart--those of the bird; for in this Class the bronchial tubes open on the outer surface of the lungs into air-cells, which are prolonged through the body into the bones. They follow the blood-vessels, and are most developed in the part of the body most used. In some lizards, as the Chameleon, the sack-like lung at its distal termination is as simple as the air-cells of a bird; but those air-cells are not comparable with the bird's air-cells, since they are not prolongations of the bronchial tubes through the walls of the lungs. And it cannot be inferred that a reptile with wings would develop air-cells like those of a bird: in the first place, because those mammals which have wings do not develop air-cells; and, in the second place, because there is nothing in existing nature to lead any one to think that reptiles might have wings. The mammalian lung is better comparable to that of a bird than is the Chameleon lung, and therefore the air-cell structure might with better reason have been anticipated to occur in the Chiroptera than in a Lizard-ally, if it were dependent on the development of wings. Moreover, among Struthious birds the legs have more of the air-cell prolongations than the wings. Therefore, being a peculiar Avian structure which only exists in association with the Avian heart and lung, it follows that because the Pterodactyle had the pneumatic foramina it also had the structures of which they are the evidence, viz. lung and heart formed on the bird plan.

Thus Pterodactyles have a nervous system of the bird type. That kind of brain only exists in association with a four-celled heart and hot blood.

They have a respiratory organization which is only met with among birds.

With that respiratory apparatus is always associated a four-celled heart and hot blood, which it would necessarily produce.

And with that respiratory organization is always associated a brain of the type that the Pterodactyle is found to possess.

_Therefore it is firmly indicated that the general plan of the most vital and important of the soft structures was similar to that of living birds._

This proposition will be incidentally proved in the following memoir, in which it will be seen that with such a common plan, is associated a diversity of details sufficient to demonstrate that these animals are not birds, but constitute a new group of vertebrata of equal value with the birds--the sub-class, Ornithosauria.

OSTEOLOGICAL COLLECTION

ILLUSTRATIVE OF THE MODIFICATIONS OF THE
ORNITHOSAURIA (OR PTERODACTYLES) IN THE
CAMBRIDGE UPPER GREENSAND.

Pectoral Girdle.

STERNUM.

Pl. 1, fig. 1.

Case. Comp. Tablet.
=J= _a_ 1

The Sternum is the key to the bony apparatus supporting the anterior limbs. In the Pterodactyles from the Cambridge Greensand it has been well figured and described by Professor Owen, who enunciated its resemblance to the sternum of birds. The sternum in Pterodactyles from the Lithographic Slate, shows its proportional size to the body. The examples found in the Cambridge Greensand have as yet shown no evidence of a composite character like that attributed to Rhamphorhynchus Gemmingi.

The sternum consists of an expanded symmetrical shield having its lateral halves, which are inclined to each other at a large angle (about 150°), contracted superiorly, behind and immediately below the synovial cavities for the coracoids. The vertical angular ridge in which the lateral portions of the sternum unite becomes elevated as it is followed anteriorly, into a strong keel. This keel or interpectoral process is highest in front of the articulations for the coracoids; but the degree of elevation varies with the species. It is prolonged upward and in front of the coracoids for some distance, becoming very massive, and the prolonged mass which is flattened from side to side, reaches laterally to the outer margins of the coracoid articulations, and on the visceral side a little between and over them. The anterior crest of the keel shows the attachment of powerful muscles.

Professor Owen has observed that only in birds are distinct synovial cavities provided for the coracoids, and that no reptile has a sternum showing characters like those seen in the Pterodactyle. These coracoid cavities are placed as in birds, close together, behind the _manubrium_, which forms the hindermost part of the keel. They are convex transversely, concave from front to back as in birds, and look upward at an angle of 35°, their main direction being outward and a little backward. Professor Owen recognises the function of the shield-shaped sternum in relation to the mechanism of respiration on the one hand, and on the other hand, for the attachment of pectoral muscles of great bulk and strength.

As is well known, the muscles of the breast in most birds consist chiefly of the 1st, 2nd, and 3rd pectoral muscles, and the coraco-brachialis.

The peculiar form of the bird's sternum appears to be due to the vertical development of the second pectoral muscle, since when the 1st and 3rd muscles are dissected off, the appearance presented nearly resembles that of the sternum in Pterodactyles. There can however be no doubt but that the third pectoral muscle, which in most birds is but feebly developed, attained a far greater bulk in the Pterodactyle, because there is evidence of its powerful insertion in the distal anterior face of the coracoid, as well as of the great lateral extension of the sternal shield to which such a muscle must--by the analogy of birds--have been attached. The peculiar lateral emargination of the sternum appears to be due to the anterior sternal termination of this muscle, caused by the outward direction of the coracoid bone.

Since the coracoids were developed outward and backward so much more than in birds, it would happen, from the apparent different direction of the second pectoral muscle, that the first pectoral muscle which in birds skirts the furculum, must have passed over the coracoid, probably pulling on its inside in opposition to the third pectoral. Either a subdivision of this muscle or a distinct muscle in the same place, in function corresponding to the subclavius muscle, appears to have been powerfully attached from the anterior prolongation of the keel of the sternum to the front face of the coracoid. It is improbable that the second pectoral muscle was undeveloped, but merely directed differently to what it is in birds, since, as will be seen, there is a process at the proximal end of the coracoid homologous with that which forms the pulley round which this muscle in birds works.

Professor Owen concludes his remarks by observing that the Pterosaurian breast-bone is in the main formed on the ornithic type. The muscles also appear to be similar to those of birds.

All the specimens are much mutilated, but all show the distinctive post-coracoid lateral emarginations, but as these are not seen in German Pterodactyles they are to be regarded as characters of a peculiar sub-order and not as characteristics of the sub-class.

The example figured in this memoir and by Professor Owen is 2-5/8 inches in antero-posterior measurement, probably about one third its entire length.

A small example in the collection of Mr Reed of York extends 1-1/4 inch in the same measurement, and by the analogy of _P. suevicus_ was more than twice that length when perfect. It is remarkable in that the coracoid facets look much less outward and much more backward than in the larger species.

The mammalian sternum is usually in many consecutive pieces like the vertebral column. The types in which it attains any size as an expanded shield are Cetaceans and the Manatee, but in these groups it has no keel and is not connected with the other bones of the pectoral girdle. The proximal portion of the sternum of the Mole is elongated and bird-like, with the shield narrower than in the typical gallinaceous birds, and with the keel similarly developed. It is connected with the humerus by small sub-quadrate bones named clavicles placed at the sides of the proximal end. The sternum in Bats usually consists of a proximal and a distal part. It is narrow except at the proximal-termination where it widens like the letter T or Y; and to the sides of the lateral prolongations are attached the long, slender, curved bones named clavicles, and a pair of ribs. This sternum develops a bird-like keel. Both Mole and Bat are regarded as differing from Pterodactyles in the bone giving attachment to the clavicles instead of to the coracoids. The proximal part of the sternum in both the living animals, gives attachment to but one pair of sternal ribs. The Pterodactyle sternum otherwise differs from the Bats in having the articulations for the coracoids close together, of a peculiar concavo-convex character, with a massive portion or keel prolonged forward in front of the coracoid articulations. The Bat cannot be said to resemble the Pterodactyle closely. The sternum of the Mole differs from that of the Pterodactyle in having a less developed shield, and in having a more developed keel which is not prolonged in front of the coracoid articulations. These examples demonstrate that resemblance in conformation is functional, and no proof of affinity.

Pterodactyles make some approach in the proportions of their sternum to Struthious birds. But the Struthionidæ have the bone thick, do not develop a keel, nor, have they an inter-coracoid process while the coracoid articulations are singularly long and narrow instead of being ovate. With other birds the Pterodactyle sternum agrees in giving attachment to the coracoid bones by synovial articulations, in the bone being shield-shaped, and supporting a more or less developed keel. The keel is chiefly developed at the proximal end, as in the Albatross, which has the bone broad; and it is prolonged in front of the coracoids exactly as in _Mergus merganser_, which sternum if a little broader in the shield and thicker in the keel would very nearly reproduce the sternum of the Pterodactyle, even to the "post-coracoid lateral emargination" of Cambridge specimens. Among reptiles the only form which suggests comparison is the Chameleon, in which however the sternum consists of an anterior and a posterior part as in the Bats, the back part narrow, and the front part a long lozenge shape, with a keel made by inclination of the sides of the bone to each other as in the Dodo, but the keel such as it is, is at the back part of the bone, and there is no prolongation in front of the coracoids as in Pterodactyle. The coracoids are broad, and are applied to the two anterior sides of the lozenge. The Crocodile has a narrow flat sternum which is prolonged anteriorly between the coracoids.

The resemblance is greater with mammals than with reptiles. From birds the Pterodactyle sternum makes no essential difference, and in the Merganser finds a close ally.

CORACOID.

Pl. 2, fig. 1-6.

Case. Comp. Tablet. Specimen.
=J= _a_ 2 1-23

Commonly the coracoid in the Cambridge Pterodactyles is anchylosed to the scapula: occasionally the bones are separate, though the separation has hitherto only been observed in the largest species. In 1851 Professor Owen, when figuring the anchylosed ends of the scapula and coracoid in Pterodactylus giganteus (Bowerbank), observed that in no part of the skeleton does the Pterodactyle more nearly resemble a bird than in the scapular arch; a view again urged emphatically in 1859 when similar fragments were described from the Cambridge Greensand. Since then perfect examples of the coracoid have occurred, which show the characters given in the following description.

The bone is long, with sub-parallel sides, sub-triangnlar in section, with the proximal end expanded exteriorly and posteriorly, resembling in form the coracoid of a bird. The front surface looks forward and outward; it is flattened, is a little convex transversely, and a little convex in length; it is rugose with muscular attachments, which terminate in a tubercle on the uppermost fourth of the front, usually near to the inner side. The middle third of the slightly concave inside margin of the front aspect, is sharply angular; the parts above and below it have the angularity rounded off. The outside margin, a little more concave than the inside margin, is sharply angular in its distal third, in which the front gradually widens to near the sternal articulation, when it contracts--the whole sternal termination of the bone being directed a little inward towards the manubrium of the sternum. The inside, which faces the opposite coracoid, is convex transversely in the lower half or two-thirds; its distal termination is carried inward. The expanded proximal end of the inside is flattened, or channelled, by the developement inwardly, at the proximal end of the ridge formed with the front side, of a long strong process homologous with that on the inner side of the coracoid in birds. The channel so formed rounds on to the proximal surface of the bone, and extends backward to the limit of the scapula; over it the second pectoral muscle may be presumed to have worked[N]. The third side of the bone is much more concave in length than either of the others; it looks backward, outward, and downward, the proximal end being turned outward and downward more than the distal end; it is a little concave transversely at the expanded proximal end. Near the distal end there are sometimes visible a few faint marks of the insertion of muscular fibres, but they are much less distinct than those made by the coraco-brachialis muscle in the corresponding region of the coracoid in birds. Throughout its length it rounds into the inner side, and the upper third rounds convexly into the front. On the most posterior part of this aspect of the proximal end is a groove terminating in a long pneumatic foramen, partly in the coracoid, partly in the scapula.

[Footnote N: The homologous process is more developed in Pterodactylus giganteus. See f. 7. pl. XXXI. Owen, Cret. Rept.]

The muscular attachments on the front aspect of the coracoid appear to be two; one large and long inserted into the inner half of the middle third of the bone, terminating at the proximal end in a tubercle. No specimen shows the distal end of the insertion. This may indicate a subdivision of the first pectoral muscle. The other insertion, if it be distinct, is long and much narrower and at the distal end of the bone. This, according to the analogy of birds, should be the third pectoral muscle; if the insertion should be but part of that to which it is distally adjacent, then the third pectoral muscle must have had an enormous developement unparalleled in birds.

The distal end of the bone terminates in a synovial articulation concave transversely, convex from front to back, in form transversely ovate: the narrow side of the articulation, like the thin edge of the coracoid, being exterior. The articulation is about three fourths of the transverse diameter of the distal end; it is at right angles with the long axis of the bone, and looks downward and a little backward.

The proximal end, massively enlarged outward and backward, presents on the proximal surface three well defined regions. The largest of these is an irregular flattened surface half ovate in form, inclined to the axis of the bone at about 45°, looking backward, and upward also, when the bone is held vertically; the mesial hindermost half of the radius of this area is occupied by a pneumatic cavity: to this surface is applied the scapula. The next largest surface is rectangular and oblong, looking upward, outward, and a little forward. The transverse aspect which looks outward being nearly half as long again as the antero-posterior aspect which looks forward; in the latter direction the area is slightly concave, in the former direction it is slightly convex; its posterior boundary is parallel with the front of the bone: this area forms the anterior moiety of the glenoid cavity, to which the proximal end of the humerus is applied.

The remaining surface of the proximal end is sub-quadrate, adjoins the two other surfaces as well as the front and the inside of the shaft, it is conically concave.

The entire bone when applied to the sternum looked outward, backward and upward.

Professor Owen remarked (1859) that the "coracoid is shorter and straighter in birds than in Pterodactyles, but is commonly broader, and with a longer and stronger anterior process."

The points in which the Pterodactyle coracoid resembles that of birds (e. g. Gallinaceæ) are the long slender triangular shaft; the concavo-convex articulation to the sternum; the convexity of the distal end in front, and its concavity behind; the posterior aspect of its scapular surface, and the pneumatic foramen.

The points in which it is distinct from birds are that the bone is not produced proximally beyond the glenoid cavity for the humerus, which, instead of being lateral as in birds, and looking outward, in Pterodactyles forms the proximal-termination of the bone. The sternal articulation is proportionally much shorter transversely in Pterodactyles, terminating in a convex margin which rounds up into the thin outer margin, as in the immature coracoid of the common Cock. It is bow-shaped in front instead of being straight, and is commonly longer than in birds. The usual ossified connection with the scapula is not entirely unparalleled in birds, the whole pectoral girdle being sometimes anchylosed into a bony mass as in the frigate bird.

In the monotremata, the only mammals in which the coracoids are separate bones, they rather recall those of Ichthyosaurus than those of any other animals, and have no connection with the sternum. The bone which represents it functionally in placental mammals is the clavicle.

In no reptile is there any structure resembling the Ornithosaurian coracoid. The nearest approximation is made by the Crocodile, in which as in the Chameleon the pectoral girdle is formed as in pterodactyles and struthious birds by scapula, coracoid and sternum. But in the Crocodile the coracoid is compressed, and expanded from side to side both proximally and distally. Distally it has no synovial articulation with the sternum; and proximally a wide process of the bone extends beyond the articulation for the humerus as in birds, only the scapula unites with the prolonged part, and the glenoid cavity looks forward and inward.

The coracoid is essentially avian in its affinities, though with peculiar characters of its own. In the German genera it closely resembles specimens from the Cambridge Greensand.

23 specimens are exhibited. Nos. 4, 10, 12, are the middle parts of shafts of left coracoids. Nos. 3-12, 22, are the middle parts of shafts of right coracoids. Nos. 2, 5, 14, are proximal ends of left coracoids. Nos. 1, 6, 8, 9, 23, are proximal ends of right coracoids. Nos. 15, 16, 17, 18, 19, 20, 21, are distal ends of left coracoids. No. 13 is a nearly perfect left coracoid, and No. 7 is the glenoid cavity for the humerus formed by a right coracoid with the anchylosed scapula.

SCAPULA.

Pl. 1, figs. 2-12.

Case. Comp. Tablet. Specimen.
=J= _a_ 3 1-17
4 1- 6
5 1- 4

Professor Owen described the scapula of Pterodactylus giganteus in 1851, and added further particulars regarding the Species from the Cambridge Greensand, in 1859; but, as with the coracoid, only the humeral end has hitherto been figured. The only example sufficiently perfect to give the length and proportions of the bone is preserved in the collection of Mr Reed, of York. This left scapula is a stout strong bone, short in proportion to its strength, of flattened ovate form in section, expanding at the humeral end into an irregular sub-rhomboid mass. It is smaller in the middle, contracting both from side to side and from back to front till the back to front measurement is 7/16 of an inch, and the side to side measurement is 11/16 of an inch, and it expands a little at the free end, which terminates in a smooth heart-shaped surface, convex in the long diameter, which measures 7/8 of an inch, and flat in the short one, which measures nearly 5/8 of an inch; it is at right angles with the inside of the bone. The sharp superior lateral outline is concave, but less so than the inferior lateral outline; into that inferior aspect of the bone the sides are more fully rounded. The flattened inner surface applied to the ribs is concave in the length of the bone, which measures 3-1/2 inches; the posterior half of which is convex transversely, the anterior humeral half is concave transversely so as to be cup-shaped, and measures in extreme width 1-11/16 inch; the outline of the transversely convex outer side in length is nearly straight, but the exterior part and glenoid cavity of the proximal end is broken away, and there only remains a small median proximal sur&ce broken at both ends, a little concave in length, measuring 5/8 of an inch, and convex in breadth measuring 1/4 of an inch.

As there is no specimen in the Woodwardian Museum showing clearly the connection of the proximal with the distal end, the specimens are arranged on separate tablets.

Humeral End of Scapula.

The humeral end of the scapula exhibits in the different species much diversity of form, spreading laterally from the shaft, and terminating in an elongated articular surface truncating the bone nearly at right angles. On its inferior border it throws out a large convex tuberosity, separated from the humeral articular surface by a deep emargination. From the tuberosity usually arises a crescentic row of muscular insertions, which is continued inward and forward over the most compressed part of the scapula towards the middle of the humeral articulation. From the superior margin, interior to the coracoid, arises a prominent ridge, the spine of the scapula, which is directed diagonally backward and downward, terminating in the middle of the outer surface, where it is bordered on the anterior aspect by a long narrow muscular attachment. Between this spine and the elevated margin of the glenoid cavity the bone is much compressed and concave.

On the inside surface of the bone there appear to be small muscular attachments in front of and behind the great tuberosity. The area between the spine and the inner surface is sometimes flattened, sometimes gently convex.

With well-marked distinctive characters in the inferior tuberosity, the pre-tuberous emargination and the thick rounded form of the bone, the Pterodactyle scapula is intermediate in character between that of a mole, a bird, and the crocodile; wanting the sabre shape of the bird's scapula, it also wants the wide expanded form of the scapula of the Crocodile, but resembles the latter in the direction and degree of developement of the spine. This modification is probably due to the outward direction and clavicular function of the coracoid, as well as to the raptorial habit of the organism.

In no living Reptile is there a scapula to be compared with that of the Pterodactyle, for besides the free end being expanded, in the crocodile, it is also thin and squamous and the bone makes a continuous curve with the coracoid as in struthious birds, and not a sharp angle as in Pterodactyles. The "spine" in crocodiles is on the anterior border of the bone and directed upward and backward, while in Pterodactyles it is on the posterior border and directed upward and forward. In the Chameleon the scapula is more elongated and narrow, narrower in proportion to its length than in Pterodactyle, but becomes rapidly wide at its union with the coracoid. It is curved in length so as to fit on to convex ribs. A scapula presenting some resemblance to Pterodactyle is found in certain Liassic Ichthyosaurs.

Among mammals a straight elongated narrow scapula is rare. The mole however has a scapula of this kind somewhat cylindrical in its proximal half and not much expanded at the free end, on which there is a small spine. The anterior emargination above the glenoid cavity in Pterodactyle is entirely mammalian, as is the anterior tuberosity above the emargination, for it entirely corresponds with what in ruminants, pachyderms and many mammals would be named the coracoid process. If that process is accurately determined it is difficult to say what this is.

In birds there is often a prolonged process on the inner side of the coracoid, which however extends interior to other parts of the scapula, and to this the furculum is attached. Such traces of a spine as are to be detected in the swan conform to the Pterodactyle.

No bird has the scapula cylindrical, even struthious birds only making an approximation to such a condition; and no birds have the scapula so straight. The bone is more avian and mammalian than reptilian; and more avian than mammalian but with strong distinctive characters of its own.

17 specimens of the humeral ends of scapulæ are exhibited. Nos. 1, 4, 6, 7, 8, 9, 11, 13, 14, 15, 17 are left scapulæ. Nos. 2, 3, 5, 10, 12, 16 are right scapulæ.

The tablet of the distal ends of scapulæ comprises 6 specimens.

Fore-Limb.

HUMERUS.

Pl. 4.

Case. Comp. Tablet. Specimen.
=J= _a_ 6 1-46
7 1- 3
8 1

There are among the fossils of the Cambridge Greensand at least two well-marked _types_ of Pterodactyle humerus, readily recognised by the forms of the proximal and of the distal ends, and by the positions of the pneumatic foramina. In the group having the ulnar ridge developed the pneumatic foramen is on the posterior aspect of the bone[O] under the ulnar ridge, as in birds; but in some of the small Pterodactyles the foramen is on the anterior surface, and on its radial side. This latter kind of humerus has the distal end more or less divided into three convex surfaces, while the radial crest is enormously developed and terminates in a smooth oblong flattened surface nearly as large as the proximal articular surface, and looking anteriorly. The distal articular surfaces are not as in birds parallel to that of the proximal end, though they agree with those of birds in being at right angles to the radial crest; this ridge in Pterodactyles being directed much further outward and backward than in birds.

[Footnote O: Professor Owen states (p. 16, 3d Supt.) that the foramen is palmar. Fig. 15. T. III. 2d Supt. shows it to be anconal.]

The largest forms of Pterodactyle all have the distal articular surface flatter, and the proximal articulation less bent back so as to look more upwards. No specimen of this kind of humerus has occurred with the radial crest preserved; but it is apparently carried farther down the shaft and not so far forward as in the other group. This latter kind of bone is shown by Prof. Owen in T. III. figs. 1, 2, 3rd Sup. Cret. Reptiles; the former kind has been illustrated in figure 5 of the same plate.

Some of the most gigantic Pterodactyles appear to have had the limb-bones as solid as those of crocodiles, and unpermeated by air; and there is no evidence that the high Avian characteristics of most of these Greensand fossils also pertained to all the previously known types from the lower secondary rocks.

The osteological series comprises 46 specimens. No. 30 is a nearly perfect right humerus. Nos. 1, 2, 5, 6, 7, 8, 9, 11, 18, 22, 23, 25, 39 are examples of the proximal ends of left humeri. Nos. 3, 4, 10, 12, 13, 14, 15, 16, 17, 19, 24, 26, 27, 28, 38, 40, 41 are examples of the proximal ends of right humeri. Nos. 20, 21, 32, 33, 34, 35, 37, 42, 44, 45, are examples of the distal ends of left humeri. Nos. 29, 31, 36, 43 and 46 are distal ends of right humeri.

No. 30 shows the entire length of the humerus to be 2-1/2 inches. It has a nearly circular shaft with a diameter of a little more than a quarter of an inch, being more slender than the corresponding bone of Pt. suevicus, which has the same length. The _proximal_ articular surface is crescentic, the anterior concavity corresponding with the concave anterior aspect of the proximal end, while the convex border corresponds to the convex posterior side of the bone, which it overhangs: it is worn, but appears to measure half an inch from the radial to the ulnar side. The ulnar ridge (which is worn) has not extended more than a quarter of an inch beyond the articular surface. The thin bird-like radial crest, arising rather more distally than the ulnar ridge, is flat on its posterior surface, and extends anteriorly for a distance nearly half as far again as the length of the proximal articular surface of the humerus. On the proximal third of the posterior face are two contiguous long narrow oblique muscular insertions. The proximal ends Nos. 22, 23, 24, 25 are examples of this kind of bone, having the pneumatic foramen radially situated on the anterior aspect near to the articular surface, as may be seen in No. 24. No. 25 shows the termination of the radial crest in an oblique oblong smooth surface, slightly convex in length and breadth, directed distally towards the ulnar side.

No. 6, 7, 13, 27, are examples of another kind of proximal end, where the pneumatic foramen is an oval hole on the ulnar side of the posterior sur&ce. The radial crest arises more distally, and the ulnar ridge more proximally, than in the small species, like No. 30.

Nos. 4, 11, 14, 16 are examples of other species with the foramen placed as in the last group, only less near to the proximal end, while it enters obliquely, being directed distally from the broad concave area proximal to it. The largest proximal ends known, such as No. 2, which though very imperfect measures 2-3/4 inches over what remains of the articular surface, appear to conform to this latter type.

_Distally_ the humerus No. 30 enlarges, widening rapidly on the radial side, which is bordered near the distal end by a sharp ridge showing a muscular attachment, while the ulnar side is rounded and rather inflated. The articular surface looks downward and in the direction of the radial process. There is a mesial concavity on the radial side which is bordered on the right and on the left by a prominent rounded condyle, and behind by a condyloid convexity. On that side which in conformity with the nomenclature applied to birds' bones, has here been named the ulnar side, the ulnar and mesial condyles are impressed with a flattened slightly concave sub-rhomboid area, which looks downward, backward, and towards the ulnar side. These characters are not well seen in No. 30, but may be effectively studied in their specific variations in Nos. 36, 37, 42, 43, 44, 45, and 46.

Nos. 20, 21, 29, 31, 32, 33, 34, 35, are examples of the distal ends of humeri of a different type. They are mostly larger than the preceding group, and correspond in characters with the large proximal ends, but appear to be separable into two groups, namely those with a pneumatic foramen on the anterior radial side near to the articular surface, and those where no pneumatic foramen is seen. Unlike the previously considered type, the ulnar side is sometimes more inflated than the radial side.

The mesial condyle in this group appears in every case to be an epiphysis, which is wanting. The radial condyle becomes a large flattened slightly convex surface looking downwards, which in some of the species, as Nos. 21 and 32 (in other respects remarkable species), shows an approach to a trochlear character on its anterior side. In Nos. 33, 34 and 35 the mesial anterior concavity becomes flattened and abuts at an angle against the flattened radial condyle. No. 20 shows the rhomboid impression on the ulnar side to be more concave and more ovate. The ulnar condyle remains a smaller but prominent tubercle directed distally. Nos. 21, 22 and 34 show a ridge developed on the ulnar side of the shaft like that on the radial side in the other group, while the radial ridge is not so near to the articular surface. The largest and smallest distal ends of humeri known, both show the characters here enumerated. The great distal end of a left humerus, figured by Prof. Owen, Pl. IV. f. 1, 2, 3 of the 1st Supplement to the Cretaceous Pterosauria, is of this kind, and though imperfect measures more than three inches over what remains of the articular surface. In the small humerus, No. 30, the width over the distal articular surface is 5/8ths of an inch. If it is assumed that the large bone was no more than 5 times the length of the small one, the entire length of the humerus would have been about twelve inches. The smallest humerus, No. 29, measures over the shaft rather more than one eighth of an inch.

The Ornithosaurian humerus has but little in common with that of any mammal. Most mammals have the proximal head of the bone hemispherical, and a pit at the distal end for the olecranon process of the ulna, while there is usually little indication of a radial crest, and the proximal and distal ends are in the same plane. In the Bat however the bone is twisted a little so that the slight radial crest looks in the same direction as the distal end, here also there is no pit for the olecranon; but the bone is sigmoid and proportionally much longer than in Pterodactyles. In the horse, hippopotamus, &c., the radial process becomes more developed but never resembles that of a Pterodactyle.

Among reptiles, the bone may be compared with lizards and crocodiles. In crocodiles the proximal and distal ends are nearly in the same plane, the distal end has two condyles, the head is convex from side to side, and the radial crest is moderately developed and never extends so far outward or so far proximally as in Pterodactyle. In the Chameleon the bone is more twisted than in Crocodile, and as in Pterodactyle the distal end is compressed on the radial side to a sharp margin. In Iguana, Scink, and Monitor both proximal and distal ends are much expanded, and the radial process makes no approximation to that of a Pterodactyle.

The bird humerus does not approximate more closely in form to that of the Pterodactyle than does the Chameleon humerus, though it has the cardinal distinction of pneumatic foramina, and these sometimes corresponding in position in the two groups.

The bird humerus is commonly longer, though in the parrots the proportions and straightness are not unlike Pterodactyle. In some respects a nearer resemblance is seen in the raptorial bird _Gypogeranus serpentarius_, in which the radial process is rather more developed than in the Crocodile, and extends further proximally though still much smaller than in Pterodactyle; here too the superior surface is concave from side to side, and the distal articulation is not unlike that of some Pterodactyles. But no Pterodactyle has the head of the humerus convex from the radial to the ulnar sides, and the bird is distinctive in having the ulnar crest developed on the inferior side of the head: a faint approximation to a similar development is seen in Crocodile, but there is no trace of such a process in Pterodactyle. The distal end is more Bird-like than Lacertian in form, but is twisted to a greater angle with the proximal end than in birds.

Altogether the bone is distinctive. The points in which it is unlike birds and reptiles are those in which Birds and Lizards resemble each other; it would not be easy to say that in form it resembles one group more than the other. But it is linked with birds by the pneumatic foramina.

RADIUS AND ULNA.

Case. Comp. Tablet. Specimen.
=J= _a_ 9 5- 6
10 1-10
11 1- 7
12 1- 4
13 5- 6

Of neither of these bones has a perfect specimen been found. While fragments of humeri are met with frequently, fragments of these bones are rare. In accordance with the analogy with birds the Ulna might be presumed to be the larger bone of the two. But from a study of German specimens the larger bone is found to be the Radius, which according to the mammalian plan is placed in front of the ulna. As a whole, the fore-arm of Ornithosaurians is only to be compared with the insectivorous mammal _Chrysochloris Capensis_, in which there are also three bones in the fore-arm,--the third bone like the _Pteroid bone_ in Ornithosaurians, extending about half-way from the carpus to the humerus, and holding, relatively, a similar position and development to the fibula in bats.

The pteroid bone articulated with a separate carpal, and was placed on the side of the arm, adjacent to the radius, which at the distal end extended in German specimens more inward than the ulna. In Chrysochloris the third bone appears to be behind the other bones, and adjacent to the ulna[P].

[Footnote P: See D'Alton and Pander _Chiropteren und Insectivoren_, Bonn, 1831, pl. 5, Chrysochloris.]

Among neither birds nor reptiles is any comparable modification of the fore-arm to be found. Then by examining the proximal surface of the proximal carpal, the characters of the distal end of the Radius are readily discovered. The proximal carpal shows on the same surface another articular facets with which however only one fragmentary distal end of a bone corresponds. That accordingly is identified as the ulna. Besides these, three other articular ends of bones occur, one of which fits on to the distal end of the femur. The remaining two are both large bones, with epiphyses which formed portions of the articular surfaces, and are usually wanting. One of these bones corresponds in form with the ulna of a bird, and would fit the facet on the ulnar side of the distal end of the Pterodactyle humerus. The other bone is massive with a sub-quadrate articular end, and might well be the proximal end of the radius. Some specimens are among the largest fragments of Pterodactyle bone known. The only other bone that either of these could be is the distal end of the tibia, a bone not yet known, but probably not unlike that of a bird.

I. Distal End of Ulna.

Four specimens which show articular ends such as the ulna should have, are mounted together. They are compressed bones with the section of the fracture elongately oval; and the shaft widens from the fracture to the articulation without increasing in thickness. The outer surface is gently convex, becoming concave mesially near the articulation; the inner surface has the same characters, only the concavity at the extreme distal end reaches from side to side of the bone. The two short sides both look outward as well as laterally; one of them flattened so as to thicken the bone, is concave in vertical outline owing to the extreme distal end turning suddenly outward; the other side a little convex, compresses the bone and inflects its inner margin. The longest specimen measures 1-5/8 inch; 5/8 inch wide at the fracture, and 1-1/8 inch wide at the distal end. The greatest thickness at the distal end is half an inch, the thickness of the fractured shaft is 5/8 of an inch.

The articular surface appears to have an elongated sub-reniform shape, the part at the compressed side of the bone being narrower than the broad ovate part on the thick side of the bone, to the lateral limit of which it extends, while the narrow part does not extend laterally nearly so far as the inflected border, which appears to give attachment to powerful muscles. There is also a strong muscular attachment at the corresponding diagonal corner of the bone where the outer surface on its right meets the side of the bone in an elevated ridge.

In its long diameter the articulation is a little convex; transversely it is very convex in the ovate part, but more flattened in its narrower continuation. Where widest it measures about 4/10ths of an inch.

Nos. 5 and 6 on another tablet appear to be distal ends of ulna of another kind of Pterodactyle. They are less compressed, more quadrate in section, and have the sides more nearly parallel The flattened side similarly has a concave border, but instead of having its distal termination developed laterally, has it thickened behind. The opposite side of the bone which in the other specimens was compressed is here thick and well rounded, and not at all inflected. There is an absence of the concavity noticed on the outer surface of the bone in the compressed specimens. The articular surface is much flatter, and a little concave in length instead of being convex; as in the other examples it looks downward. The largest fragment. No. 5, measures 1-3/8 inch long; it is 6/8 inch wide at the fracture, and 4/8 inch thick. The sub-quadrate distal end is more than an inch long, more than 4/8ths inch thick on the thick side, and nearly 4/8ths inch thick on the compressed side.

II. Distal End of Radius.

The best preserved of the 10 specimens here exhibited is 3 inches long, No. 2. The shaft is oval, flattened on one side; measuring at an inch from the fractured end 7/10ths of an inch in the least diameter, and one inch in the wide diameter. It widens distally at first slowly, then rapidly, till at the articular end its greatest width is two inches. But while expanding laterally it contracts from side to side, the more convex side of the two at about an inch from the articular end, beginning to approximate to the flatter side till the articular end has a short diameter of less than half an inch.

On the left-hand corner of the convex inner side of the bone is an elevated flattened disc for muscular attachments, fully half an inch in diameter, there is a slight muscular attachment interior to this, nearer the middle of the bone. The left-hand corner of the flattened outer side of the distal end of the radius is marked by a vertical ridge bordering a similarly elevated oval muscular attachment. Parallel to this nearer the middle of the side is a much stronger and acutely elevated ridge.

The articulation is made up of three distinct parts, all in a straight line. The portion of bone adjacent to the large muscular disc is compressed and rounded on the distal end; then first there is a rather deep circular cup 3/8ths of an inch wide, nearer to the more convex than to the flatter side of the bone; adjacent to this cup is a convex ball of about the same size; while the remainder of the articulation is concave in length, convex from side to side, and looks downward and a little towards the inner convex side of the bone. The specimens are arranged so as to display these characters.--The example described is of nearly the same size as that figured for the humerus in fig. 1, T. XXIV. of the Cretaceous Reptilia. The less well preserved bone in that figure exhibits the Ulna in its true position behind the Radius.

III. Proximal End of Ulna.