Part 6
The tablets of this bone comprise 22 specimens. Nos. 2, 3, 4, 5, 6, 8, 9, 10, 15, 16, 19 and 22 are so mounted as to exhibit the proximal surface. Nos. 7, 11, 12, 13, 14, 15, 16, 20 and 21 show the distal surface of the bone. No. 17 is a cast from the distal sur&ce of a proximal carpal for comparison with the proximal surface of the distal carpal. No. 16 is a cast from the proximal end of the wing-metacarpal for comparison with the distal surface of the distal carpal. No. 20 is a distal carpal of unusual type, 19 is a cast from its proximal surface, and 21 is a cast from the distal surface of the same specimen.
The proximal aspect of this bone is rather narrower than the distal aspect; each is sub-triangular in outline, the sides being convexly curved. In the long axis from the apex on the inside to the short outer[Q] side the bone is convex proximally with an oblique transverse depression; in the short axis, that is, between the two longer sides, the middle of the bone is hollow, but the oblique transverse depression makes both sides of the hollow convex,--so that excepting the smooth unarticular triangular area adjacent to the apex, the sub-quadrate articular surface is shaped somewhat like two cones put side by side in such manner that the apex of each touches the base of the other: the apex of that cone which should touch the short side or base of the triangle formed by the bone, is truncated by a depression which exhibits an oval pneumatic foramen. Towards the apex, on the same side as the pneumatic foramen, the margin of the bone is rounded for a small terminal oval articulation which looks outward and upward.
[Footnote Q: Outer and inner are here used in accordance with the usual interpretation, and the better to compare with birds.]
The lateral aspects of the bone are at right angles to the proximal and distal surfaces. They are smooth, a little concave in antero-posterior extent, and convex in the opposite direction. That one on to which the marginal articular surface impinges is except for that surface sub-quadrate in outline; the opposite side has a slightly crescentic form, the flattened outline being distal. They show several small foramina.
The distal aspect of the bone is comparatively flat. The distal surface consists of a smooth unarticular part adjacent to the apex, rather smaller than the corresponding area on the proximal aspect of the bone. Between this part and the sub-crescentic articular surface, which occupies the remainder of the distal area, is a large circular pit, furthest removed from the side of the bone which forms the sub-apical marginal articulation. The pit on the apical side shows several small foramina; on the outer side of the bone the roughened articular surface extends down the pit side. The articulation is flattened from side to side of the bone. Its outer margin is slightly prominent, and the margin of the pit is slightly convex and prominent, so that the intervening articular surface in the direction between these limits is concave. It is commonly divided into two parts by a median band limiting a depressed half, which is in a slightly different plane from the other half of the articulation. Where the depressed part terminates towards the marginal articulation, which does not extend so far distally, there is between the two a small step-like roughened articular portion.
The large crescentic articulation described gave attachment to the wing-metacarpal bone; if there was a second metacarpal terminating in a claw, it must have been attached to the small articulation last referred to. In No. 20 the pit is extremely small, the impressed part of the articulation is small and deeply sunk, while the apicular articulation is widened and shortened so as to make the outline of the bone quadrate.
III. Lateral Carpal.
The tablet exhibits eight examples of a bone which at its distal end is attached to the marginal apicular articulation of the distal carpal, thence extending proximally, and terminating in an articular facet for the third bone of the fore-arm, so as to overlap laterally both of the other carpals. The bone is compressed, is three times as wide as thick, and in outline sub-quadrate with a distal talon. On the inner side it is flat, and on the outer side above the talon it is concave vertically and convex transversely in such way that the side of the bone to which the distal articulation is adjacent is thicker than the other side, and sometimes bent at a sharp angle. The talon on the inner aspect of the bone is flat and continuous with the quadrate side, but on the outer aspect it is separated from the side by an elevated transverse thickening, distally to which the bone is compressed, and rounded into the adjacent parts. The talon extends over more than half of the distal end of the bone, and constitutes with the remainder of the distal end, the distal articulation, which is flat from front to back, and concave from side to base. The proximal articulation is cupped and extends over the whole proximal surface; it is at right angles with the sides of the bone. Both the inner and outer sides exhibit small pneumatic foramina. No. 8 differs from the other specimens in its sub-triangular lateral outline, and general less complex modifications.
The Carpus of the Cambridge Ornithosaurians at first sight is not easily compared with that of Birds; Birds having but one bone between the radius and the metacarpus. But that one bone in the Ostrich, for instance, is not unlike in form to the proximal carpal of Pterodactyle; while the proximal end of the metacarpus presents so close an analogy with the distal carpal of the Pterodactyle, that even were it not easily demonstrated that the bone in Birds commonly called the metacarpus is a carpo-metacarpus[R], it would be strong evidence for such a determination. In Birds there is a small lateral bone between the ulna and carpo-metacarpus which is evidently homologous with the lateral carpal of our Pterodactyles, and so, since this lateral carpal of the Ostrich is the pisiform bone, it results that the lateral carpal of Pterodactyle is the pisiform bone also. From this follows a conclusion of the first importance in the interpretation of the hand. The fine hair-like metacarpals of the Pterodactyle are on the side towards the pisiform bone, while the great wing-metacarpal is on the side towards the index finger.
[Footnote R: They separate without difficulty in the Chicken.]
In Birds the rudimentary thumb (or second finger, according to Owen) has no connection with the carpus. In the Penguin, _Aptenodytes Patagonica_, it has disappeared altogether, and there then remain two fingers of which the outer one (seen from the front as we have placed our animal) is the larger, and has the greatest number of phalanges, precisely as in Ornithosaurians. Moreover the wing-metacarpal, in the Penguin especially, is seen to unite with the carpus directly under the radius, as is the case with the Cambridge Ornithosaurians. Hence it follows that in Pterodactyles the thumb is not developed, and that the wing-finger is not the little finger, but the index finger, precisely as in Birds. If Goldfuss gave a reverse arrangement it was because the hand in his specimen, as is proved by the claws, was upside down. In the immature state the distal carpal of Pterodactyle appears to have been composite.
Notwithstanding the opinions of eminent German philosophers to the contrary no reptile has a carpus comparable to that of the Pterodactyle. If some of them have two rows of bones and a pisiform bone, so have mammals, and the mammalian arrangement is not more like the Ornithosauria than is that in Reptiles.
METACARPAL BONE.
Pl. 6.
Case. Comp. Tablet. Specimen. =J= _b_ 5 1-3
The illustrations of this bone comprise 31 specimens. Nos. 1 to 15 are examples of the proximal end, and Nos. 16 to 31 show the distal trochlear end of the bone. No. 1, which is nearly entire, gives the form and proportions of the wing-metacarpal in one species, but a knowledge of its variableness in German forms would guard against an assumption that all the other Greensand species were to be restored on the plan of this example. It is 3-5/8 inches long, to which three-eighths of an inch may be added for the distal articulation, making the length up to 4 inches. The proximal end is not well preserved, but in its wide measurement is 5/8ths of an inch; the distal end in the same measurement is about 3/8ths of an inch. A large example from the Chalk, in the Museum of C. Moore Esq. of Bath, shows the bone more attenuated distally. No. 1 is compressed so as to be oblong in section at the proximal end, and ovate in the middle of the shaft, which is slightly smaller than the distal end. One of the lateral outlines is straight; the other is concave. The bone is straight. In No. 30 the shaft where thickest measures less than 1/4 of an inch, becoming nearly circular in section. The shaft of No. 31 measures nearly an inch in width at its distal end, rather more than half an inch in thickness. No. 10 is 1-1/2 inch wide at the proximal end and 7/8ths of an inch thick. No. 9 would not have measured less when perfect than 2-1/2 inches over the proximal end, so that if it had the proportions of No. 1 it would have measured when entire not less than 16 inches in length.
The Proximal End.
The proximal end has never been figured. Prof. Owen's figure pl. IV. fig, 4-5, First Supt. Cret. Rep. is probably part of a jaw, and not the wing-metacarpal. The articular surface is oblong with one corner rounded off so that the adjacent long and short sides become confluent on the exterior surface of the bone.
In the middle of the flat inside margin and extending proximally is a semi-cylindrical process, which is prolonged a short distance down the side of the bone as an elevated ridge. On the flattened articular end this process is bordered by a semicircular furrow which extends half-way across the bone, outside of which is a slightly convex semicircular band which extends to the outer margin of the bone, except towards the short side opposite to that one which rounds into the outer side, where there appears to be a narrow unarticular area. On the inside of the bone where the two ends of the semicircular proximal furrow terminate are two deep grooves which extend a short distance distally; they are both limited by inward extensions of the short sides of the bone, that crest being most developed in height and length which is toward the flattened short side. The outline which these modifications give to the inner side of the proximal surface is intermediate in form between the letters S and [sideways M].
The Distal End.
The distal end has been figured by Prof. Owen in the British Fossil Mammals, p. 545; in Dixon's Geology of Sussex, Pl. XXIX. fig. 12; Cret. Reptiles, Pl. XXXII. figs. 4 and 5, First Supt. Pl. IV, fig. 9-11, and other places, and fully described. It closely resembles the distal end of a bird's tibia; and consists of a pulley-shaped end set obliquely on to the compressed shaft, which just above the junction is reniform in section, owing to the development of _a median rounded ridge_ on the same inner side of the bone which bears the median ridge at the proximal end, while on the opposite side there is a corresponding _median depression_ which does not extend far proximally. In this depression is an oval pneumatic foramen; on the right of the median ridge of the other side, but placed more distally, is another pneumatic foramen. The median ridge has sometimes a slight furrow on each side. It terminates proximally in strong muscular insertions, which extend round the right side of the bone; and distally, becoming more elevated and rounded, it curves obliquely to the rights and forming one of the sides of the pulley, passes round the base as three quarters of a spiral, the termination extending laterally beyond the shaft. On this side of the bone, distal to the median depression, arises another ridge strong and well rounded, which is directed to the right, similarly passes round the base as a spiral, and forms the other side of the pulley. It is not so prominent as the border previously described. While the spirals approximate at their origin, they become widely separated at the base, making the articulation wider than the shaft. In No. 31 the three inches of the shaft which remain show both pairs of its sides sub-parallel; the widest measures nearly an inch; the base of the articulation is less than a quarter of an inch wider.
Limited to the base, between the two outer ridges of the pulley, is a short median ridge slightly developed; so as to flatten the middle of the concavity between the ridges, and divide it into two grooves. The degree to which the middle ridge is developed varies in different species. In No. 30, the smallest pterodactyle, remarkable for a long wing-metacarpal bone, it is not to be detected. The exterior sides of the trochlear articulation are broad, flattened, and a little concave.
There is some variation in the way in which the shaft is set on the trochlear end. It being often in the middle, but not unfrequently inclined more to one side than to the other.
The metacarpus finds no close parallel among living animals. The thread-like metacarpal bones suggest the condition of the hind-foot in the Kangaroo. The predominant metacarpal suggests the ruminants. But the nearest approximation is found among birds where the bone for the middle finger is large and the bone for the third finger is slender. This may be observed (among other examples) in the Penguin and the Swan. But here the parallel ends. The proximal end in Birds, we have already seen to be hidden by the anchylosed distal row of the carpus, and the distal end though often convex from side to side never presents the trochlear joint of the Pterodactyle. Consequently so far as regards the form of the articular ends the resemblance is closer with Reptiles and clawed Mammals than with Birds. In Birds the small metacarpal is usually of similar length with the large one as is the case with Pterodactyles.
FIRST PHALANGE.
Pl. 7.
Case. Comp. Tablet. Specimen. =J= _b_ 6 1-10
No perfect specimen of the first phalange has been found in the Cambridge Greensand. Ten bones are mounted to illustrate it, all of them less perfect than others in the series of associated bones. No. 1 shows the heel of the proximal end; Nos. 9 and 10 are portions of the proximal articulation from which the epiphysis which forms the articular heel-part seen in No. 1 has come away. Nos. 2 to 8 are the distal articular ends of first phalanges. It is improbable that any of them belong to the second phalange, since they agree in form, and show muscular attachments which correspond.
Prof. Owen has figured the shaft of a fine example of this bone in Dixon's Geology of Sussex, Pl. XXXIX. fig. 11. A good proximal end is shown in Pl. XXXII. fig. 2, of Prof. Owen's monograph of the Cretaceous Reptilia, but the figure appears to have been previously given in Pl. XXIV. fig. 2 of the same monograph. By far the grandest specimens are drawn in Pl. XXX. Prof. Owen names these wing bones. In the "Literature of English Pterodactyles" the loss of the proximal epiphysis from the specimen represented in Prof Owen's fig. 1 and 2 led me to interpret the bone as an ulna. Figs. 1 to 4 represent the proximal ends and greater portions of the shafts of first phalanges. The lower bone in fig. 5 is neither radius nor ulna, as stated in the text of the Cretaceous Reptilia, but the shaft and distal end of a first phalange; the upper bone being the second phalange.
The Proximal End.
The straight shaft throughout its length is triangular in section. One side of the bone is gently convex; this may be named for convenience the outside. The two parts which make up the other side are inclined, and have the angle in which they meet rounded; one part looks upward and inward, the other downward and inward. Towards the proximal end the bone widens and thickens, and the moiety of the inner side which is away from the heel becomes cleft, and has the sides of the depression rounded to form a large pneumatic foramen. The articular surface looks upward and a little outward on the side of the pneumatic foramen. It consists of two semicircular concave grooves, separated by an intervening low convexity. The outer of these grooves extends from the margin of the extreme proximal point of the heel to the widest point of the bone; the other groove more deeply concave, is a third shorter, extending from inside the pneumatic foramen to the heel. Here both grooves converge, terminating in a point, exterior to which a little distally is a hemispherical mammilate eminence. On the distal side of the eminence there is a depression so as to make the angle behind the heel almost hemispherically rounded. This articulation fits on to the distal articulation of the wing-metacarpal.
When the proximal epiphysis forming the heel comes away, it leaves a large sub-circular pit with a depressed narrow border.
Distal End.
On nearing the distal end, the angle of the inner side of the shaft becomes more depressed; and the articulation becomes an elongated oval, slightly convex transversely and convex in length so as to extend distally in a curve in such way that the articulation looks downward and outward from an aspect of the bone exactly opposite to the aspect from which the proximal articulation looks upward and inward. Hence the two articular surfaces are sub-parallel; but the distal one at its distal termination is bent inward, so as to make the adjacent lateral outline of the bone concave on the inside at its termination. The articulation does not cover the most proximal part of the distal surface.
SECOND PHALANGE.
Pl. 7.
Case. Comp. Tablet. Specimen. =J= _b_ 7 1-14
On this tablet are mounted 14 specimens. Nos. 1 to 9 are examples of the proximal end of the second phalange. If there were more than two phalanges, of which there is no osteological evidence, it is possible that proximal ends of succeeding phalanges may be included with these. They all however resemble each, other so closely as to lend no support to such a supposition. Nos. ?10 to ?14 have been mounted with the proximal ends because they appear to be portions of the middle of the shaft of the second phalange; they indicate a rapid distal attenuation, favouring the idea of there being but two phalanges.
The proximal end of the shaft has the outer side flattened, rarely concave, commonly slightly convex; the inner side being much more inflated, and not dissimilar in form to the inner side of the first phalange. Proximally the bone widens and one lateral outline extends outward in a curve, on the inner side of which, under the proximal articulation, is placed the pneumatic foramen. The elongated oval articular surface is concave from side to side and concave in length; it does not extend in length so far as the straight side outline, exterior to it being a crescentic flattened or convex area. The distal end attenuates more rapidly in some specimens than others, and appears in Nos. 11, 12, and 14 eventually to become cylindrical; but none of the specimens show its distal termination.
The phalanges of the wing-finger attain a grand development in length which is not paralleled in Birds, nor surpassed in Bats. In the Ostrich there are three phalanges in the wing-finger, while in Ornithopterus there are two joints, and in other German Pterodactyles four joints. The terminal joint in the Ostrich is a claw, but in Pterodactyle the terminal joint appears to be unarmed as in ordinary birds. The form of the bones in being compressed from side to side is more bird-like than bat-like. But the claws in their compression from side to side are more like the bat than the bird.
DISTAL END OF METACARPAL
or Metatarsal Bones.
Pl. 6.
Case. Comp. Tablet. Specimen. =J= _b_ 7 1-14
Sub-cylindrical bones, apparently elongated, and a little compressed obliquely, terminating distally in a slightly expanded trochlear articulation. Some of them show on one side marks of an osseous adhesion: this has led to their being regarded as claw metacarpals rather than as the distal ends of tibiæ. But on the supposition of their being claw metacarpals, they are as compared with the same bones in _Pt. Suevicus_, out of all proportion large, since wing-metacarpals from the Cambridge Greensand would not as a rule have a diameter more than twice that of these bones. The trochlear articulation is smaller in proportion to the shaft than in the wing-metacarpal, and usually shows a pit at the side and grooves above for ligaments; the mesial pulley groove is shallow and broad. Seven specimens are mounted in illustration, of which No. 3 may be regarded as doubtful. It is possible that they may be metatarsals.
CLAW PHALANGE.
Pl. 8.
Case. Comp. Tablet. Specimen. =J= _b_ 8 1-3
These three sub-triangular bones, which supported the claws, are much compressed from side to side, and consequently deep. The superior outline is convex from front to back and rounded from side to side. The inferior outline is concave from front to back, sometimes narrower, sometimes broader than the upper part of the bone, while the inferior aspect is always more flattened than the superior aspect. On each side on the lower half of the bone is a deep groove. The articular end is divided into an upper articular part, which extends as far down as the lateral groove and a lower non-articular part with ligament markings. The articulation is concave from above downward, and is divided into two lateral parts by a mesial vertical ridge. The articular end is about half as deep as the bone is long.
Pelvic Girdle and Hind Limb.
OS INNOMINATUM.
Pl. 8.
Case. Comp. Tablet. Specimen. =J= _b_ 10 1-9
Nine specimens are mounted in illustration of the pelvic girdle: Nos. 1, 3, 4, 5 and 6 show the acetabular or femoral aspects. The right os innominatum is exemplified by Nos. 1, 4 and 5; the left by Nos. 3 and 6. No. 2 shows the sacral aspect of a left ischium, and its attachments with the pubis and ilium. No. 8 is the sacral aspect of a left os pubis. No. 9 is the femoral aspect of a right OS pubis. None of the specimens are sufficiently complete to give the form of any of the bones. The only known example of an entire or nearly entire pelvis at all comparable in form, is seen in the original specimen of Dimorphodon macronyx figured by Buckland, _Trans. Geol. Soc._ Ser. 2. vol. III. p. 217. In nearly all the fossils from the Cambridge Greensand the bones of the pelvis are anchylosed together.
The ossa innominata have been determined as right and left on the supposition that the pelvis of the Dimorphodon is in situ, and from the general correspondence of the form of the constituent elements with elements of the pelvis in the lower mammals, reptiles, and birds.