710 



COMPARATIVE ANATOMY 



also numbered from one to five, have in some cases special names. The 

 thumb (digit 1) is the pollex, the corresponding great toe being the 

 hallux, while the fifth digit is called minimus, the second finger in the 

 hand the index, and the fourth the annulus. 



From this typical condition all forms of chiropterygia legs, arms, 

 wings are derived by modification, fusion, or disappearance of parts. 



^c.l.calc. 



c. 



II 



V IV 



Fig. 421. The skeleton of the left fore- and hind-feet of a rabbit. 

 A, fore-foot ; B, hind-foot. 



a.. Astragalus ; c.l, first distal carpal or trapezium ; c.2, second 

 distal carpal or trapezoid ; c.3, third distal carpal or os magnum ; c.4,5, 

 fused fourth and fifth distal carpals or unciform ; ce., centrale ; ce' ., 

 centrale of hind-foot or navicular ; cm , fibulare or calcaneus ; im., in- 

 termedium or semilunar ; me., metacarpals ; met., metatarsals ; ph., 

 phalanges ; ra., lower end of radius with its epiphysis ; r.c., radiale or 

 scaphoid ; t.2, second distal tarsal or mesocuneiform ; .3, third distal 

 tarsal or ectocuneiform ; .4, 5, fused fourth and fifth distal tarsals or 

 cuboid ; u.c., ulnare or cuneiform ; ul., lower end of ulnar with its 

 epiphysis; I.-V., digits. (From Borradaile). 



C. Hindlimb of the frog tadpole shortly before metamorphosis. 



centr, centralis ; cl.calc., cartilaginous calcaneus ligament ; c.l.tars.s., 

 supplementary cartilaginous tarsal ligament ; c.ses., sesamoid cartilage ; 

 F, fibula ; fib, fibulare ; pr.h., prehallux ; ses, sesamoid bone ; T, tibia ; 

 t.ach., tendon of Achilles ; tars, II and ///, second and third tarsals ; 

 tib, tibiale; I-V, phalanges. (After Tschernoff). 



The more distal a part is, the more variable it is ; reduction takes place 

 on the margins of the appendage, the axial portions being the last to 

 disappear. Occasionally, in various groups (amphibia, mammals) there 

 occur what are interpreted as rudimentary additional digits prehallux, 

 prepollex, and postminimus but their status is uncertain. There are 

 also certain membrane-bones developed in the appendages, such as the 

 patella (knee-cap) in some reptiles, birds, and many mammals, in the 

 tendon that passes over the knee joint, the fabellae in the angle of the 

 knee of a few mammals, and the pisiforme in the carpus of man and some 

 other mammals. 



