Part 6

In the axis vertebra (Pl. V. figs. 12 & 13) the posterior articular surface, concave vertically, and 3 lines in that extent at its middle part, is very convex transversely, being continued upon the sides of the posterior part of the centrum; a thick obtuse hypapophysis (fig. 13, hy) descends below this surface: the anterior or odontoid surface presents the usual form in birds; the odontoid process (ib. x) has a pit at its apex. The prezygapophyses (fig. 12, z), of very small size, project from the outer and fore border of the neural arch, with their articular surface looking outward and slightly upward; a ridge is continued from their back part to the base of the postzygapophyses: the surface (fig. 13, z′) in these, 4½ lines in long diameter, is three times the size of the anterior one; it is concave transversely, and looks downward and a little outward. The anapophyses (ib. fig. 12, a) are large tubercles rising above the articular surfaces. The base of the neural spine, 9 lines in length (ib. ns), is coextensive with the neural arch; the spine rises posteriorly to a height of 6 lines, with a thickness of 2 lines, having a convex upper margin (Pl. III.).

The relative size and position of the cervical vertebræ, as coadjusted in the position and degree of flexure of the neck represented in Sir Hans Sloane’s life-size painting of the Dodo, in the British Museum, are given in Plate III. with the varying proportions of the pleurapophyses and other processes.

Ribs. (Plates III. & IV.)

The specimens of ribs include both vertebral and sternal portions; that which appears to be the second or third on the right side (Pl. IV. figs. 7, 7 a) is 4 inches 4 lines in length (following the outer curve), and expands to a breadth of 7 lines at its lower part; the interval between the articular surfaces of the head and tubercle is 6 lines. The appendage (ib. a) has coalesced with the middle of the hind margin of the shaft. The neck is compressed, with a thin upper margin; the lower one is continued with a curve upon a strong internal buttress-like ridge (ib. b), which runs to near the fore part of the flattened body of the rib, where it meets the ridge continued from the tubercle, about 2 inches down the rib: there is a shallow channel between these ridges, contracting to their confluence. The inner surface of the rib is impressed by a deeper and broader channel behind the buttress: the posterior border expands in the form of a triangular plate, with a base of about an inch in extent, due to the complete confluence there of the epipleural process. The anterior border is thicker, and is almost straight. Towards the sternal end the pleurapophysis contracts and thickens, terminating in a rough syndesmotic elliptical surface, 3 lines by 2 (fig. 7, f), for the attachment of the hæmapophysis or sternal rib.

A vertebral rib (ib. fig. 2) which is entire, measures 9 inches in length (following the outer curve). The head and tubercle are at the same distance as in the preceding, but the tubercle is broader. The characters of the body of the rib are very similar; but it is narrower, not attaining a breadth of 5½ lines at its lower end; the narrowing and thickening to the articular surface for the sternal rib is more gradual.

A last vertebral rib is adapted, by the longitudinal extent and partial division of the tubercle, to the vertebra which forms the first of the coalesced series of sacrals; and the body of the rib, instead of preserving the regular outward curve of the antecedent ones, is more suddenly bent soon after it emerges beyond the margin of the ilium; the lamelliform part thence continued is straighter, and, moreover, shows upon its outer surface a flattened facet, indicative of pressure or friction by the movements to and fro of the thigh over a rib in such position. Beyond this surface the rib curves in a way not shown in the other specimens; the distal end has the flat syndesmotic articular surface to which had been attached a hæmapophysis not reaching the sternum. In this last (eighth) free rib there is no epipleural process, nor any definitely marked ligamental surface on the posterior margin indicative of the attachment of such process.

The body of a posterior vertebral rib (Pl. IV. fig. 10) shows a fracture which has been healed, with some irregular ossific deposit on the inner surface. All the ribs have a pneumatic foramen (ib. figs. 2, 7, 8, p) at the fore part of the neck, near the base of the tubercle.

The eight left vertebral ribs (Pl. III.) and the five right ones do not, either of them, constitute a consecutive series, but have come from different individuals, of different sizes, as exemplified in the third rib figured in Plates III. and IV.

The sternal ribs (P. IV. figs. 3 & 12) are characterized by the two facets, nearly or quite meeting at an open angle, into which their sternal end expands (ib. fig. 3, c). One of these ribs, which is entire, shows the single, elliptic syndesmotic surface at the opposite end (ib. b); it is 3½ inches in length, with a greatest breadth of 5 lines, and is straight. Another and longer specimen (ib. 12) shows a moderate degree of curvature. A third specimen is 6 inches in length: the proximal end has a breadth of nearly half an inch (the penultimate rib in Pl. III.).

Five successive sternal ribs are indicated by gradational size and curvature, and a sixth, which does not reach the sternum. Before describing this bone I shall proceed with the account of the sacral vertebræ, and the expanded hæmal arches of such as complete the pelvis.

Pelvis. (Plates III. & VII.)

The pelvis of the Dodo is chiefly remarkable for the flatness and great breadth of the posterior half, corresponding with the characteristic proportions of that part of the body in Pl. I. fig. 2, and in the old woodcuts of the Dutch “Dodaersen”. It includes sixteen coalesced sacral vertebræ, with which the iliac bones are continuously confluent.

The first sacral shows the transversely extended and concave articular surface of the centrum (Pl. VII. fig. 1, c); the subcircular pit (ib. p) for the head of the rib is behind the middle of the side of the centrum, at its upper part; the inferior surface is ridged lengthwise; and a transverse low but sharp ridge defines the posterior boundary, the depressions in front of which indicate the hindmost origins of the subvertebral muscle (longus colli?). The anterior outlet of the neural canal (ib. n) is subcircular in one specimen, vertically elliptic in others, and 3 lines or less in transverse diameter. From the sides of the neurapophyses stretch out the strong buttresses of bone which blend with the under part of the ilia, giving off from the fore part of their base the præzygapophyses (ib. z), and from the back part of their apex the surface (ib. d), or part of it, for the tubercle of the last moveable rib, the ilium in the latter variety affording the rest of that surface. The fore part of the strong neural spine (ib. ns) is roughened by a syndesmotic surface; it rises to a height of 14 lines, curving forward, and is confluent at its summit with the approximated anterior margins of the ilia. A continuous track of bone, forming a smoothly obtuse longitudinal ridge, represents the summits of the succeeding sacral spines (ib. fig. 2, ns) to the hindmost vertebra of the series, without any trace of their primitive division; but this track rises, posteriorly, above the shallow channel on each side, in which are the foramina (ib. o), indicating most of the constituent vertebræ.

The second sacral vertebra abuts against the ilium by a pleurapophysis (ib. fig. 1, pl 2), as well as a diapophysis (ib. d 2); but the former is a slender, straight filament, or narrow plate of bone, confluent at both ends.

In the next two vertebræ the pleurapophysis (ib. pl 3 & 4) assumes more breadth and robustness, but is short and straight, abutting against the inner surface of the ilium an inch in advance of the acetabulum. The first of these rib-buttresses inclines forward, and is completely confluent with the ilium; the thicker one (ib. pl 4) has retained part of its primitive ligamentous attachment to the ilium: the proportions of both are subject to some variety.

These are succeeded by three or four vertebræ in which the pleurapophysis is not developed, the attachment to the ilia being by diapophyses only (ib. d d), which are short slender lamellæ, directed upward and backward; below and between them are the double orifices for the separate motory and sensory roots of the sacro-spinal nerves. In the next vertebra the pleurapophysis (ib. pl 8) reappears, longer but more slender than in the fourth sacral, extending obliquely backward, and expanding at its extremity to abut against a prominence on the underside of the ilium, opposite the hind part of the acetabulum, with which prominence the rib has completely coalesced by an expanded end. The under part of all these vertebræ is traversed by a sharp median longitudinal ridge, which is more feebly and interruptedly continued to near the end of the sacral series.

Eight vertebræ, abutting by diapophyses only (Pl. VII. d d) against the ilia, succeed the one last described; their coalesced bodies are less than half the breadth of those of the preceding vertebræ: they gradually diminish in depth to the last, without loss of breadth. The diapophyses proceed obliquely outward and backward, are lamelliform, about 9 lines in length, and intercept oblong cavities of the same extent and direction, into which open the orifices (ib. fig. 2, o) noticed on the upper surface of that part of the pelvis. The articular surface of the body of the last sacral is transversely elliptic, 4 lines by 2 lines, and very slightly convex. The outlet of the neural canal, above it, is circular, and about a line in diameter, the whole vertical extent of the last sacral being 5 lines, while that of the first sacral is 2 inches 2 lines.

The ilium is divided, as usual, into two parts by the ridge on its upper or outer surface (ib. fig. 2, r), extending obliquely backward to behind the acetabulum—the anterior division being narrower and concave, the posterior broader and convex but in a minor degree. The anterior (slightly thickened) border of the ilium is curved with the convexity forward, extending 8 or 9 lines in advance of the fore part of the neural spine of the first sacral vertebra. The ilia almost meet above that of the second and third sacrals, with which they coalesce, and then diverge to the oblique boundary ridge, which is thence continued, in some with an angular bend, more directly outward. At this angle the bone is so confluent with the sacrum that the orifices leading to the ileoneural canals are almost or quite obliterated. These canals are, here (ib. i ï), the longitudinally extended cavities intercepted between the fore parts of the ilia and the continuous coalesced sacral spines and diapophyses, widening to their anterior outlets. The extent of that part of the ilium in advance of the acetabulum is 3 inches 8 lines; the breadth at its middle part is 2 inches. As the ilium approaches the acetabulum it increases in thickness, and is grooved at the outer margin by a vessel which leaves impressions of its ramifications upon the upper concave surface of the bone (ib. fig. 2, +62+). The acetabulum (ib. a a) is circular, 11 lines in the diameter of its outlet, 9 or 10 lines in that of its inner circumference, being widely open, as usual in birds, towards the cavity of the pelvis; the trochanterian surface (ib. t t) above the acetabulum is elliptic, with the long axis lengthwise, 9 lines by 6 in its diameter, with its upper border sharp and produced; the anterior border (ib. b) of the acetabulum is slightly produced; the position of this articular cavity is about midway between the fore and hind ends of the pelvis. The oblique external ridge of the ilium terminates in the outer margin of the broader part of the bone (ib. r′), 7 lines above the sharp and prominent margin of the trochanterian surface (ib. t). The ilia have diverged from each other for the extent of an inch and a half behind the beginning of the boundary line (ib. r), which interval is occupied exteriorly by lateral ossification from the neural spines to the diapophyses of that part of the sacrum: the mesial borders of the ilia (ib. fig. 2, 62′) slightly converge to the fifteenth sacral vertebra, where they are separated by an interspace of 1 inch, and then again diverge to the last sacral; they coalesce with the diapophyses (ib. fig. 2, d d). The inner or under surface of the ilium is thickened into a kind of buttress (ib. fig. 1, e), terminating behind the ischiadic foramen. The breadth of the iliac bones and intervening sacrals, 1 inch behind the acetabulum, is 5 inches; at the back part of the pelvis it is 4 inches. The outer border of the posterior part of the ilium (ib. fig. 2, g) projects as an obtuse ridge above the ischiadic foramen and the succeeding expanded and confluent part of the ischium (ib. 63), which is vertically concave externally: the ilium, ischium, and pubis (ib. fig. 1, 64) have completely coalesced around the acetabulum. The pubis, which in this part is 7 lines thick, contracts as it becomes free to a diameter of 4 lines; it is smooth and convex below, and has been broken off near the acetabulum on both sides; the fracture shows its pneumatic structure. The ischium, as it recedes from the acetabulum, contracts to a trihedral column, with a vertical diameter of 4 lines; it is concave outwardly, convex inwardly, and suddenly expands below, about an inch from the acetabulum, to form part of the posterior boundary of the obturator foramen (ib. fig. 1, f), which is 9 lines in length, and is situated one half in advance of, and the other half beneath, the ischiadic foramen (ib. m). This latter is oval, with the large end forwards, 1 inch 3 lines by 10 lines in its principal diameters. Behind this foramen the ischium is confluent with the ilium for an extent of 2 inches, or perhaps rather more, as the posterior margin of the pelvis is not entire in any of my specimens. The inner surface of the ischium forms a low, obtuse longitudinal ridge towards the pelvic cavity, losing thickness as it recedes from the acetabulum. The chief pneumatic foramina in the pelvis are on the inner surface, above the acetabulum, behind the trochanterian articulation, and behind the iliac confluence of the last sacral pleurapophyses,—also at the hinder part of the ilium, on each side of the transverse buttress (ib. e) near its posterior junction with the ischium. The prærenal fossa (between pl 4 & pl 8, fig. 1) is deep and subdivided by the diapophysial plates: the postrenal fossa is wide and shallow.

Sternum. (Plates III., IV., VI., XI.)

Of this instructive and determinative bone there are two specimens, the one most entire (Pls. III., IV. fig. 4, & VI.) measuring in a straight line, from the costal process to the hind border, 7 inches. The extreme breadth between the lateral processes (Pl. IV. h) is 4½ inches; from this diameter the bone contracts anteriorly to a breadth of 3½ inches at the costal processes (ib. d), and posteriorly it contracts more rapidly to an obtuse, horizontally flattened apex (Pl. VI. fig. 3). The anterior border of the sternum (Pl. IV. fig. 4) is widely and rather deeply emarginate at the middle (e), less deeply so on each side: the breadth of the mid notch (b e b) is 1 inch 9 lines, that of each side notch (b d) is 1 inch 2 lines. The sternum is deeply hollowed above (Pl. XI. fig. 4), correspondingly convex beneath (ib.); the keel (s) is low and thick, commencing by a pair of broad obtuse ridges (Pls. IV. fig. 4, & VI. fig. 1, r r) from the mesial ends of the outer walls of the coracoid grooves (ib. b′), which gradually rise from the surface of the bone as they extend backward, converging to form the beginning of the keel about 2 inches from the anterior emargination (e): the keel gains a depth of ¾ of an inch at the middle of the sternum, then gradually sinks to the level of the bone, as it extends backward, at 1½ inch from the hind end (Pl. VI. fig. 3), a little increasing in thickness as it subsides: its free border describes a pretty regular convex curve (Pl. III.); it is thick, flat, partially canaliculate: the sides of the base of the keel expand, to be continued gradually into the body of the sternum (Pl. XI. fig. 4). Behind the costal surface (Pl. VI. c), on each side, extends a lamelliform process (Pls. III. & VI. h), ½ an inch in breadth, upward and a little outward, slightly expanding to its free termination, which, however, is not entire in either specimen: the longitudinal extent of this characteristic process, where it is best preserved, is 1 inch; it is conjecturally restored in Plate III.; it answers to the ectolateral process (h) of the gallinaceous sternum (Pls. III. & XII. fig. 3): there is no trace of an entolateral process (ib. i). The thin margin of the Dodo’s breast-bone, behind the ectolateral process (Pls. III. & VI. h), is entire and uninterrupted to the obtuse apex, and the body of the sternum is imperforate: the notch (f) behind the process (h) represents the ectolateral notch of the gallinaceous sternum (Pl. XII. figs. 1 & 3, f). The costal border (Pl. VI. fig. 2, c) is 1 inch 9 lines in extent, and 6 lines across its broadest part; it shows articular surfaces for five sternal ribs, of which the four posterior (2–5) are bilobed, the anterior one (c 1) simple, and limited to the outer half of the border; the second sternum shows some variety in this respect: the deep interspaces, in both, are perforated by pneumatic foramina. The costal process (d) in advance of these surfaces expands, as it rises upward and a little outward and forward, to the extent of nearly an inch; the hinder and outer side is impressed by a concavity, continued from the costal border; the inner side is smooth and convex: it is not quite entire on either side. The coracoid grooves (Pl. IV. fig. 4, b b′) are small in proportion to the sternum, and are divided from each other by an interspace of about an inch; the outer wall of the groove (b′), 9 lines in extent, is moderately produced and convex; it appears to be a continuation of one of the initial ridges (r) of the keel: the inner wall of the groove (b) is deeper, and is formed by the obtuse angle of the anterior border of the sternum, between the medial and lateral emarginations. External to each coracoid groove is a large elliptical pneumatic foramen (p) or depression. There is no episternal process. On the convex outer surface of the body of the sternum the “pectoral” ridge (Pl. VI. fig, 1, k) is feebly indicated, extending from the outer end of the coracoid groove backward and inward to near the posterior third of the keel. The concave surface of the sternum (ib. fig. 2) shows a number of small pneumatic foramina, chiefly along the middle line to near the posterior third. Behind the costal border the substance of the sternum gradually increases in thickness from the sharp lateral margins to the middle, above the base of the keel, and shows there a fine pneumocancellous texture (Pl. XI. fig. 4).

Scapular Arch. (Plates III. & VIII.)

This consists of the scapula (Pl. VIII. figs. 6, 7, 8 & 9, 51), coracoid (ib. figs. 4 & 5, 52), and clavicle (ib. 58), the latter ending in a point and here tied by ligament to its fellow, to form a furculum. I have received the elements of this arch in three conditions:—one in which the bones, though of full size, are separate; a second, in which the scapula and coracoid are confluent, but the clavicle distinct; a third, in which the three bones are confluent at the ends converging to the humeral articulation. The scapula (ib. figs. 6, 7, 8 & 9, 51), 3 inches 7 or 8 lines in length, has the usual sabre-shaped body, slightly expanding and decurved at its free extremity, the breadth of which is 7 lines: it terminates obtusely: varieties of shape are shown in figures 6 & 8. The outer surface of the bone, at the two posterior thirds of its extent, is slightly concave and marked by muscular attachments; the inner surface of that part is smooth and slightly convex: the bone increases in breadth, with some diminution of thickness, towards the articular end, and is remarkable for sending off from the lower border, at 7 or 8 lines from that end, a short process (ib. 51); between this process and the articulation the breadth of the bone is little more than 3 lines; the breadth of the articular end is 9 lines. Nearly one-half of it is occupied by the almost flat, subcircular humeral surface (fig. 8, a), with a diameter of 4½ lines, and directed upward, outward, and a little forward. From this is continued an oblong, much narrower coracoidal surface, beyond which the acromial process (fig. 6, c) extends forward, curving toward the coracoid, and terminating obtusely.

The coracoid (ib. figs. 4, 5, 8 & 9, 52), averaging a length of 3 inches 7 lines, expands to a breadth of 1 inch 3 lines at its sternal end (52), of which the articular surface (e) occupies an inch; the non-articular part forms the outer angle (m), and extends in advance of the pneumatic foramen (Pl. IV. fig. 4, p) at that part of the breast-bone: the outer border which extends from this free angle to the body of the bone, into which it subsides, at one-third of the extent of the bone, is sharp; the inner border is obtuse to near the inner angle (Pl. VIII. figs. 4 & 5, n). The outer surface of the expanded sternal end is smooth and convex; the inner surface is flatter and more irregular, perforated by pneumatic foramina; the diameter of the subcylindrical part of the shaft is 4 lines: the extremes of difference in the distal expansion of the coracoid are shown in figs. 4 & 8, 52, Pl. VIII. A muscular ridge and rough surface (ib. fig. 9, r) mark the back part below the middle of the shaft. The bone then expands to its upper articular end, which is obliquely truncate from within outward: it shows, first, the oblong surface for the scapula, which is extended upon the inner prominence of that end; next, the larger and full oval surface for the humerus (h), from which the thick, obtuse, inner continuation of the scapular end projects inward, forward, with a slightly upward curve, and shows the narrow oblong surface for the articulation and ultimate confluence of the clavicle (58). The coracoid unites with the scapula at an angle of 100°.

The clavicle (ib. figs. 4 & 5, 58), at its scapular end, is slightly expanded, compressed, with an obtuse recurved termination articulating with the above-named surface of the coracoid, and in one instance coalescing therewith, and by extended ossification with the “acromion scapulæ” (ib. figs. 8 & 9). As the clavicle descends it curves slightly and contracts to a point. The angle at which the pair meet is shown in figs. 4 & 5.

Bones of the Wing. (Pls. III. & VIII. figs. 12–17.)

Of the humerus the series contains two specimens, both measuring 4 inches 3 lines in length, one right, and the other left (Pl. VIII. figs. 12–14), but differing slightly in their proportions and in colour—one being of the olive-brown tint with which most of the bones are stained, the other black. The articular head (ib. a) is an elongate oval convexity, with the larger end toward the radial side, prominent toward the back and rather flattened toward the front of the bone, which there swells out beyond the base of the articular surface. The radial tubercle is small, and descends from the radial end of the head for about 5 lines; the pectoral process (ib. b) is triangular, obtuse, short, and bent, or directed toward the front side of the bone: the ulnar tuberosity (ib. c) is more produced in that direction; it is oblong, obtuse, with its base impressed by a large pit both above (fig. 12, h) and below—the lower one (ib. g) being the deepest, and perforated by a pneumatic foramen; the convex, broad, ulnar border of this tuberosity has two slightly produced processes, an upper or posterior (ib. fig. 12, c) and a lower and internal (ib. g), which is the smallest. The breadth of the proximal end of the humerus, across the tuberosities, is 1 inch 5 lines, beyond them the bone contracts to a smooth subcylindrical shaft, showing at the back part of the proximal third a longitudinal ridge (fig. 12, r), half an inch in length; it gradually expands at the distal third to a breadth of 10 lines, where the articulations offer the usual avian characteristics of the elbow-joint. The head of the humerus is occupied by a fine cancellous structure: into the large vacuity below this, crossed in the section figured (Pl. XI. fig. 5) by a transverse slender bar of bone, the small pneumatic foramina at the bottom of the wide and deep fossa for the axillary air-cell open. The part of the hollow proximal end giving off the pectoral and other processes for the attachment of muscles is strengthened by similar abutments. The pneumatic cavity of the main part of the shaft of the humerus is simple, with a compact wall thicker than at the ends of the humerus, but not exceeding that which is characteristic of the long air-bones in birds. The portion of the distal end chiefly serving for muscular attachments and the antibrachial articulation are also cancellous.

The radius (Pls. III. & XII. fig. 15) is a straight and slender bone, 3 inches 1 line in length, and 2 lines in chief diameter of the shaft. The proximal articular surface is subcircular, 3 lines in diameter, moderately concave; the distal end expands to the same extent, but is compressed, as usual.

The ulna (Pls. III. & VIII. figs. 16 & 17) is 3 inches 1 line in length, of the usual ornithic character, with a well-defined, narrow, elliptic, rough muscular depression, 8 lines in length (fig. 16, c), extending upon the shaft from below the anterior or palmar angle of the proximal articular surface. This bone has no pneumatic foramen; the orifice for the medullary artery is above the middle of the same palmar surface, the canal inclining distad. The shaft of the bone is nearly straight; the back or anconal surface, which is slightly convex, shows feeble impressions of the attaching ligaments of the alar plumes, which are represented in all the figures of the entire or living bird. A second ulna is 3 inches 3 lines in length.