OSTEOLOGY AND ARTHROLOGY 45 



row ; trapezium, trapezoid, os magnum, and unciform, in 

 the second. The number of these bones is not the same 

 in all animals on account of the coalescence or absence of 

 some. In each row the bones are placed side by side, with 

 the exception of the pisiform, which being placed on the 

 palmar surface of the cuneiform, produces a small pro- 

 jection in man, but a very pronounced one in quadrupeds. 



The pisiform is called the hooked hone in some veterinary 

 anatomies. If we consider the hook which it forms, we 

 may recognise that the name is appropriate ; but from 

 the point of view of comparison with the human carpus, 

 the name is unfortunate, for it creates confusion between 

 the true pisiform (the fourth bone in the upper row), and 

 the last bone in the lower row, which is the veritable unci- 

 form bone. We do not here seek for similarity of form, but 

 homology of regions ; and it is only by using the same 

 names to denote the same things that we can succeed in 

 determining such homology. 



Taken as a whole, the bones of the carpus form a mass 

 which, by its superior border, articulates with the bones 

 of the forearm, and by its inferior border is in relation with 

 the metacarpal region. Its dorsal surface (anterior in 

 quadrupeds) is slightly convex ; its palmar surface (pos- 

 terior in quadrupeds) is excavated, and forms a groove in 

 which pass the tendons of the flexors of the fingers. This 

 last, in man, has the appearance of a gutter, because of the 

 prominences caused by the projection of the internal and 

 external bones beyond their fellows. 



In quadrupeds the palmar groove is especially determined 

 by the pisiform bone, of which we have just mentioned the 

 great development. 



The region occupied by the carpus, in the unguligrades, 

 is known as the knee ; it would have been more appropriately 

 named had it been called the wrist. 



The number of the metacarpal bones in mammals never 

 exceeds five, but it often falls below it ; the same is true 

 for the digits. The first are generally equal in number to 

 the latter ; an exception is met with in ruminants, whose 

 two metacarpals coalescing soon after birth, form but 



