716 Proceedings of the Royal Society of Edinburgh. [Sess. 
by Gegenbaur, and their substitution for the older descriptive terms 
(adopted from human anatomy in the writings of anatomists as eminent as 
Owen, van Beneden and Flower), have greatly facilitated the description 
of this region ; the graphic formulae employed by Leboucq, Max Weber, and 
Ktikenthal, which I have also used in this memoir, enable the eye to follow 
the description and assist one in recognising the morphology of the carpal 
bones in the manus of the Cetacea. 
The guide to the solution of this problem is to be found in a manus in 
which the number of disto-carpalia corresponds with that of the digits ; 
whilst in specimens in which some carpalia are wanting, it is important to 
study the articulations of those which are present with the metacarpal 
bones. 
As previously stated, Hyperoodon provides us with the necessary 
key, for in this carpus each metacarpal, in the majority of specimens 
examined, has a definite disto-carpal for articulation with it. The 
researches of Ktikenthal and Leboucq into the development of embryos 
of several species of Cetacea have shown that, in the early stages of Beluga 
and Monodon, a fifth differentiated cartilage existed in the distal row, 
which was not represented by a bony C 5 in the fully formed carpus, so that 
in the progress towards ossification this carpal element had disappeared.* 
A similar defect has also been observed in the carpus of a few specimens of 
Hyperoodon ; the missing bone was carpale 5 , and the formula of the distal 
row was reduced in them to carpalia 1 , 2 , 3, 4- 
Are we to assume that either five carpalia constitute in the Cetacea 
generally the normal number of elements in the distal row in the very early 
stages of development ; or that a carpus may be formed at its initial develop- 
ment in which the elements of the disto-carpalia are fewer than five ? In the 
latter instance the diminution in number would be a fundamental develop- 
mental defect, and could only be satisfactorily determined by the study in a 
given species of a sufficient number of specimens at the commencement of 
and in the early stages of cartilaginous differentiation in the carpus. In the 
former case the deficiency would be due to the disappearance of the cartila- 
ginous precursors of the bones, either by atrophy in the early stages of 
development, or by fusion between adjoining cartilages or bones at somewhat 
later stages. The fusion might take place : a, between cartilages or bones 
in the same row ; b, between cartilages or bones in the distal with those in 
the proximal row ; c, between the disto-carpalia and the metacarpals. 
* Gervais, in his part of the great Osteographie des Cetaces by Van Beneden and himself, 
figured the manus of a foetal Hyperoodon in which five cartilages were present in the 
distal row, but he regarded the fifth of these as a pisiform. 
