| OCR Text |
Show 808 DR. J. MURIE ON PHASCOLOMYS PLATYRHINUS. [June 27, same specimens. In P. latifrons the same flattening underneath of the bodies of the lumbar vertebrae occurs as in the dorsal region, but the bodies altogether seem stronger than in similar-sized Wombats. In P. platyrhinus the transverse processes of the lumbar vertebrae are immensely long. The first and last are shorter than the two middle ones. The hindmost three are wider than the sacrum. Compared with those of P. latifrons they are narrower antero-posteriorly and somewhat rounder. The size being less in P. wombat, they otherwise correspond to what has been said of P. platyrhinus. All the examples of P. latifrons, none of P. platyrhinus, and only one of P. wombat exhibited short suturally connected pleurapophy-ses resting upon the diapophyses of the first lumbar vertebrae. If other proof were wanting of the termination of the dorsal and commencement of the lumbar vertebrae in P. latifrons, the presence of these pleurapophyses in P. wombat, where fifteen ribs exist, would satisfy objections which might be raised, that in P. latifrons their more regular occurrence indicated a greater number than thirteen ribs as the normal condition. Sacrum.-In defining the number of sacral vertebrae present in specimens of the Common Wombat, Prof. Owen remarks*, " If we regard those vertebrae only as sacral which join the ossa innominata, then there are but three"-more often, it will be found, only two. If, on the other hand, anchylosis is the test, then the sacral vertebras may vary from 3 to 4-5, or even as many as 7, in number in different specimens. I am inclined, however, to agree with a further statement of the same anatomist, that four are the normal number of bones (Cat. Coll. Surg. p. 330). Besides the fact that the four vertebrae succeeding the lumbar ones have transverse processes directed almost straight outwards, or the posterior two of them even somewhat forwards, in contradistinction to the vertebrae behind, which have transverse processes inclined at an angle backwards, there is the still more cogent reason, that the sacral plexus passes through the three foramina, bounded by the usually coalesced four sacral elements. This division between true sacral and caudal vertebrae is remarkably well seen in specimens of P. latifrons, where the transverse processes are shorter and less liable to anchylosis than in either of the other species. The sacral vertebrae of P. platyrhinus are chiefly distinguishable from those of P. wombat by the greater width of the transverse processes and by their unusual flatness both on the pelvic and dorsal surfaces. The extent of the auricular surface abutting against the ilia is relatively greater ; and, as compared with most specimens of P. wombat, the base of the sacrum and anterior edge of the first transverse process reach somewhat further forwards on the ilia. These conditions appear to give greater lateral and longitudinal capacity to the cavity of tbe pelvis ; indeed it is the width and flattening of the dorsal surface of the sacral region of the pelvis continued backwards towards the tail which produces the characteristic hinder * Trans. Zool. Soc. vol. ii. p. 396. |
