100 ItlE. W. H. FLOWEE ON THE OSTEOLOGY OF 



rib, is effected, not in this case by the disappearance of either the lower or the upper 

 attachment, but by their gradual coalescence. 



In Plata nista the attachment of the ribs is again different in detail, being something 

 between that found in the true DelpJiinidce and in Ima. Each of the first seven ribs 

 is attached to the transverse process of its own vertebra and to the body chiefly of 

 the preceding vertebra; but the transverse processes differ from those of the Del- 

 phinidm in being very short, and in being more rapidly transferred down to the 

 bodies; indeed this takes place as early as the sixth vertebra, and before the disap- 

 pearance of the articular facet for the head of the rib, leading to a blending of the two 

 articulations in one as in Inia. 



The remaining vertebrae (lumbo-caudal) are twenty-one in number. In accordance 

 with the usual (and most correct custom) of reckoning the caudal region of the Cetacea 

 as commencing with the first vertebra which bears a chevron bone*, there are but three, 

 or at most four, vertebrte, which can properly be called lumbar. The uncertainty rests 

 upon the difficulty of determining, in a skeleton of which the bones are all separated, 

 and in which, owing to its immaturity, the articular surfaces and processes are not very 

 distinctly marked, to which of the vertebrse the first (always very small) pair of haema- 

 pophyses was attached. I think, however, that there can be little doubt that the 

 fourth of the vertebrae behind the thoracic region did bear such bones, not only from 

 indications on its own surface, but also because the facets on the hinder edge of the 

 under surface of the fifth are too strongly pronounced to be the attachments of the 

 small first pair. Taking, then, the true lumbar vertebrae at only three, Inia presents 



* As a uniform system of nomenclature in enumerating the vertebrce of Cetacea is veiy desirable, it is to be 

 regretted that Esohrioht and Eeinhardt, in their most recent works on Cetology, should have given the weight 

 of their high authority to reckoning as the last of the lumbar vertebrae the one immediately preceding the first 

 chevron bone, and which has commonly been regarded as the first caudal. The only reason given for this 

 change is, that "the anus, which may justly be said to mark esternaUythe limits between the abdomen and the 

 tail, is situated directly beneath the fli'st chevron bone " '. This, however, does not prove the case ; for if we 

 look at the skeleton of any terrestrial mammal in which the distinction between the different regions of the 

 vertebral column is definitely marked, we may see that the commencement of the caudal region is situated some 

 way in front of the position of the anus. We ought rather, according to this criterion, to reckon two or three 

 of the vertebrae in the Cetacea commonly called lumbar to the region of the tail, — a view further strengthened 

 by the fact that, in the ordinary mammals, the chevron bones, when present, begin generally not on the fii-st, but 

 ou the second or third caudal vertebra. Such a division would, however, bo quite impracticable. 



Each chevron bone belongs essentially to the vertebra in front of it. This is most clearly seen when they are 

 small, as in the commencement of the series. In the skeleton of a Physeter that I lately examined, the first is 

 even ankylosed to the posterior edge of the body of its proper vertebra, and has no connexion with that behind 

 it. It is quite certain that any vertebra bearing a chevron bone cannot consistently be regarded as one of the 

 lumbar series. We may therefore conveniently reckon the first vertebra which is so distinguished as the com- 

 mencement of the caudal region. 



' Recent Memoirs on the Cetacea, published by the Eay Society, 1866 ; Eschricht and Eeinhardt on the 

 Greenland Whale ; p. 105 ; and Eeinhardt on Psciidorca crassiclens, p. 204. 



