640 CETACEA. 



digits liave the appearance of being thus applied, viz., the first to a single bone on 

 the pre-axial side of the radius ; the third to a carpal wedged in between the radius 

 and ulna ; the fourth and fifth digits to the extremity of the ulna itself ; whilst the 

 second finger is applied to the single representative of the distal row of carpals. 



In the case of a manus with six carpals, there can be little doubt that the bone 



wedged between the radius and ulna is the os intermedium or lunare, which has two 



bones lying, the one external to the other on its pre-axial side. As I have shown, 



these two bones are united in certain carpi, and we are, therefore, entitled to regard 



the one as the scaphoid or radiate, and the other as the trapezium, a view 



which appears to be fully borne out by their development. In the foetus, in which 



the carpus is like a piece of cartilaginous mosaic work, each carpal element having 



in its middle its little ossific centre and its limits defined by the septa of articulation, 



two such distinct carpal elements, placed one before the other, intervene between the 



radius and the base of the pollex. This arrangement in the foetal difl'ers from 



what I have described in the adult manus, in that these two pre-axial carpal elements 



are separated from each other by a transverse, instead of a longitudinal, articulation ; 



and in that the external of the two is the more anterior, and is wholly excluded from 



touching the radius of itself, supporting the pollex as a true carpal in development 



and form ; whereas in the adult it stretches from the metacarpal pollex to the radius 



with the other pre-axial carpal element wedged in between it and the os intermedium. 



As already mentioned, these two bones are occasionally fused into one in comparatively 



young mani, which entitles us to conclude that in the foetal manus they were 



represented only by one cartilage and ossific point. But it is when the two elements 



are distinct and divided transversely, and when in that condition the more distal of 



the two supports not only the pollex, but has also the metacarpal of the second finger 



applied to it, that the true nature of this distal element becomes apparent. Under 



these circumstances, it cannot well be regarded as a metacarpal. Eurthermore, as the 



carpals for the support of the second and third fingers form two quadrangular bones at 



the bases of these digits, and as the os intermedium and os radiate or scaphoid are 



unmistakable, the conclusion seems unavoidable (in this aspect of things at least) 



that the distal element is a trapezium. If so, it follows that when it is elongated 



and reaches the radius it is also the same bone, and that the element internal to it is, 



of course, the scaphoid or radiate, facts which are supported by the history of their 



development, and further that a trapezio-scaphoid can only be said to exist in 



Tlatanista when these two elements are united in one, an abnormal occurrence in 



this dolphin. 



The basal free bone of the pollex would thus appear to be a metacarpal, and as 

 such in the six-carpaled manus is applied to the extremity of the trapezium, and 

 touches the pre-axial side of the trapezoid. 



The four remaining carpal bones are all nearly of one size and more or less 

 quadrangular. The trapezoid projects sHghtly beyond the bones which support the 

 third and fourth digits, and is in contact with the metacarpal of the pollex, the tra- 

 pezium, the OS radiate, os intermedium, os magnum, and outer edge of the third 



