600 OSTEOLOGY OF LAEID^. 



one for the head of the metaciirpus. Its superior non-articular surface is grooved for 

 the passage of the extensor tendon. 



The uhiar qarpal or so-called pisiform hone is very large. The notch on its metacarpal 

 aspect is exceedingly broad and deep ; so much so that the bone is saddled, as it were, 

 on the inner ridge of the metacari)al articulating surl'ace, along which it rides freely. 

 The inner prong of the bifurcation is greatly elongated ; the outer is shorter and 

 stouter ; and it is by the extremity of this that the bone chiefly articulates with 

 the metacarpus. The ulnar articulating surface is merely a slight oval depression. 

 The apex of the bone is tolerably acute, and rough for the attachment of tendons. 



The composition and movements of the wrist-joint, as Avell as those of the elbow, 

 afford an interesting study; but as there is nothing in them peculiiU' to the group 

 under consideration, I pass them over with the foregoing brief description. 



The metacarpal segment of the arm is about half the length of the autibrachium. 

 The two piincipal bones of which it is composed arc. entirely separate, except at their 

 extremities, where they are firmly consolidated. Of those the radial one is much the 

 largest, the ulnar being merely a delicate cylindrical shaft, somewhat broadened and 

 flattened toward its proximal extremity. The main shaft of the bone is rather flat- 

 tened than cylindrical. The superior edge of the proximal extremity bears a short but 

 unusually prominent and well-developed crest, with a tuberculated apex, for the at- 

 tachment of the extensor tendon. Its distal extremity is abruptly truncated, for 

 the articulation of the pollex. Just at its base, on the inner or under aspect of the 

 bone, is a small osseous projection, either for the attachment of a tendon or the confin- 

 ing of some that go to the digits. The articnlatiug face of the bone is very long, ex- 

 tending from the superior border over the head, and some distance along the inferior 

 aspect. It is tran.sversely deeply concave, having raised borders, the inner and most 

 prominent of which is received in the bifurcation of the " pisiform" bone. 



The pollex is simply a small, slender, straight, compressed spiculum of bone, movea- 

 bly articulated with, and projecting directly from, the truncated extremity of the 

 metacarpal crest. The "ulnar finger" in like manner projects from the extremity of 

 the ulnar segment of the metacarpus, being closely bound to the under surface of the 

 fiist phalanx of the radial finger. 



The radial finger, or the proper continuation of the limb, consists of two ])hiilanges 

 only, each rather more than half as long as the metacarpus. The first of these some- 

 what resembles the metacarpus, in being wide, thin, and compressed, and partially di- 

 vided into two longitudinal parallel segments. The distal is simply a straight, slender, 

 tajiering and acutely-pointed siiiculum, articulating with the preceding by a somewhat 

 enlarged head. 



OssA INKOMINATA. — The jjelvis has, for a natatorial family, considerable depth and 

 concavity. Anteriorly it is flat, its parietes very deficient ; but posteriorly the large 

 ischia project downward and backward, forming extensive and solid walls ; while me- 

 dially there is a subrectangular deep fossa formed by the vaulting of the innominate 

 bones for tlie reception of the renal organs. 



The ilia are rather small and thin bones projecting as far forward as the seventh 

 dorsal vertebra. The dorsum is slightly concave in every directiou ; the venter is 

 about flat; the external margins deeply concave; the anterior broadly convex ; the 

 internal meetiug and being anchylosed with its fellow and with the superior sacral 

 spines over the median line. It receives the transverse processes of the sacrum against 

 its inferior surface and inner margin. Toward the posterior border, and opposite the 

 acetabulum, the bone spreads out and becomes much arched and expanded, to form 

 with a similar enlargement on the anterior portion of the ischia, the chief part of the 

 concavity proper of the p: Ivis, that wh'ch contaius the kidneys. 



The ischia stretch downward, backward, and outward, as broad, thin planes, flat, ex- 

 cept at the commencement near the acetabulum, where they are vaulted. The proper 

 " tuber ischii " is mex'ely a small projection on the posterior margin of the bones ; what 

 is properly the "ascending ramus" continues directly onward and forms the real ex- 

 tremity of the bone, which is remarkably elongated and tapering. The ischiadic notch 

 is, as usual, converted into a foramen, in this case very large, subcircular, situated just 

 posterior to the acetabulum. 



The pubis is merely a long, thin, flexible, nearly straight spiculum of bone, a little 

 curved inward, and dilated at its floating extremity. It commences at the acetabu- 

 lum, which, as usual, it contributes to form, and runs backward, outward, and down- 

 ward, lying parallel to the anterior edge of the ischium and abutting against, but 

 being quite disconnected with its extremity. Thus the obturator foramen is converted 

 into an exceediugly loug, deep, narrow notch, resulting from the concavity of the border 

 of the ischium being applied against the straight edge of the pubis. Perhaps, how- 

 ever, the real obturator is to be found iu a small oval or subcircular dilatation at the 

 apex of the notch, which is wider than the notch itself, partly shut oft' from it by lig- 

 aments, and, with its edges, thickened and smooth. 



The acetabulum is situated at the confluence of the three pelvic bones, just at the 

 middle of the inferior border. As usual, it is a simple ring, entirely deficient internally, 



