478 



Vertehrata. 



bones are either moTable,* or are immovably bound together ; in the 

 latter case they often fuse with increasing age. The carpus 

 consists of two transverse rows of bones ; in the proximal row there 

 are usually three bones, in the distal, four, the two outer bones of the 

 typical five (fourth and fifth distal carpals) being fused.f At the 

 outer edge there is a rather large sesamoid bone, the pisiform. Of 

 the five digits, the poUex (first) has two phalanges, the others each 

 three ; only in certain, much modified forms (Whales), is the number 

 increased. In certain Mammalia the poUex is more freely movable 

 than the other fingers, so that the hand is a prehensile organ ; where 

 it has not this function it is usually reduced, or altogether absent. 

 Other fingers also may dwindle or vanish, particularly if the limbs are 

 specially adapted for walking or running (Ungulata) : with the 

 decrease in number, there is an increase in power on the part of the 

 remainder ; in such cases a fusion of metacarpals may occur. The 

 structure of the fore limb shows great variety in correlation with 

 the varied function (digging, climbing, flying). [See also the 

 special descriptions). 



The pelvis is peculiar in that the ilia are directed backwards; 

 the point of attachment to the sacral vertebrse lies towards its anterior, 



Fig. 389. 



Fig. 390. 



Fig. 389. Left half of the pelvis of a, young Omithorynchus. I acetabulum, il iUum, 

 is isohium, 'p pubis, x point at whiob the isohium and pubis unite behind, m marsupial 

 bone. — Orig. 



Fig. 390. Left half of the pelvis of a new born Calf, oc point at which ischium and 

 pubis unite with one another below ; the other letters as in the preceding figure. — Orig. 



* The lower end of the radius, with the hand (which is only connnected at a 

 definite spot with the ulna, elsewhere with the radius), can then swing outwards ; this 

 is especially the case in Man. 



t The oarpals of Mammalia are usually distinguished by the following names ; the 

 proximals from within outwards, scaphoid, lunar, and cuneiform; in the 

 distal row, trapezium, trapezoid, magnum, and unciform. In some 

 cases (by reduction of the number of metacarpals), some ' of these bones may be 

 absent ; or fusions may occvir. Occasionally a centrale is developed between the 

 rows. 



