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Show 1902.] OF THE SHORT-XOSED SPERM-WHALE. 57 The two ends are rough and evidently had cartilaginous continuations. One end is broader than the other, and is apparently the lower extremity : one surface is flat, and this I take to be the external surface ; the other is very convex from side to side (see PI. II. fig. 2, a), meeting the flat surface in a more or less sharp edge; one edge, the anterior, being much sharper than the other. The general form of this little bone agrees very closely with the shape of that region of the 12th rib just distal of the curvature; here the outer surface is flat and the inner surface convex, the outline of a transverse section being (as shown in PI. II. fig. 2, a) similar to that of the above small bone. Further, I discovered a narrow, curved cartilage, four inches (100 mm.) in length, pointed at one end, truncated and slightly excavated at the broader end, which fitted on to the broad end of the small bone. There is no doubt in m y mind but that this bone and cartilage constitute part, and the greater part, of the 13th rib of the left side ; the upper end of which must have been connected to the 13th thoracic vertebra: the connection was probably by means of cartilage, for this narrower upper end of the bone is rough and convex. On re-examining this vertebra, I noticed that the end of the transverse process is similar to that of the 12th, and unlike that of the succeeding vertebra, in that it has a small articular surface on the left side, but none on the right side. W e have here, I think, an explanation of the discrepancy as to the number of thoracic vertebra?; for, except in a very carefully macerated skeleton, this little bone would undoubtedly be overlooked ; and in skeletons lying on the shore there is little likelihood of this last rib being found. Wall's figure, however, is erroneous in that he places the last rib (the 14th according to his enumeration) in line with the loiver end of the preceding; but from the form of the bone and its resemblance to that part of the preceding rib, I think that it lay higher up, in the position indicated in PI. II. fig. 2, with a long strip of cartilage below, and a shorter cartilage (which I did not succeed in recovering) above. In Wall's specimen this last small rib measured 1| inches, and the preceding rib 11| inches. Krefft, too, notes that the last rib, the 13th, is but 4 inches in length, whilst the preceding is 12 inches. It is not stated whether the measurement of the rib was taken along the curve, or in a straight line from the capitulum to the free end, but presumably it was in the former manner. In m y specimen the 12th rib is 9*6 inches (235 mm.) along the outer curve, or in a straight line 8| inches (215 mm.), and the bony part of the 13th rib is H inches (37 mm.). I estimate that the total length of this rib" with both upper and lower cartilages, was about 8 inches (200 mm.). W e may then conclude that in Cogia there are 13 thoracic vertebra?, with 12 pairs of complete ribs articulating with the |
