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Show 1870.] ANATOMY OF THE PRONGBUCK. 367 spinal muscular fossae deep. Between the last lumbar and first sacral vertebral lamina there is a large lozenge-figured interspace. The funnel-shaped sacrum has a length of 3} inches ; and its anterior transverse diameter is almost as much. The sacro-iliac synchondrosis is formed by a single articulation of the foremost vertebral element; it possesses but a diminutive neural process. The three hinder vertebrae belonging to the sacrum are partly anchylosed, and possess spines subequal in height; their transverse processes are anchylosed, so as to form a tapering vertical plate of bone parallel with aud as high as the neural spines. The caudal vertebrae, as already mentioned, were imperfect, five alone being present, the small terminal factors having been lost. Those extant, together 4 | inches in length, were remarkably porous, evincing a diseased condition or atrophy of the cancellous tissue. The first or anterior caudal possessed broad transverse processes of bony plates, but gave off no backwardly extending zygapophyses; the remaining vertebral bodies diminished in size, but each had long slender prominent spicula passing distally. Fig. 9. Ventral view of the sternum and sternal ribs. p. st. Presternum, m. st. Mesosternum. x. Xiphosternum. (b) Chest.-The eight elementary constituent parts of the sternum are partially coalesced, so that it appears to be composed of but five separate pieces. Of these the foremost are narrow, stout, and cylindroid, the middle and hindmost on the contrary wider and thin. The manubrium or prsesternum (p. st) of Parker* is bifid anteriorly. It is a short stout bone, with an upward projecting boss between the first two ribs. The thick vertically narrow second and the rather wider third elements are ossified together; the fourth and fifth expand in breadth but diminish in thickness. The sixth, seventh, and eighth fcetal segments are firmly united, the seventh or post-mesosternal being the broadest of the whole series. The xiphosternum or ensiform piece (x) is a long, flat, and strong process of bone, narrowing considerably at its distal and finally truncated extremity. Eight sternal ribs or costal cartilages on each side abut against the lateral margins of the sternum. The ribs number thirteen pairs, of which eight are true and five false. The first two are nearly straight or with but slight arching. * ' The Shoulder-girdle and Sternum in the Vertebrata,' Ray Soc. 1868. |