18 MAMMALIA. 



metatarsal bones of the principal toes in the leaping animals are 

 long, and partly united together, e. g. in the Kangaroo, Pedetes, 

 Dipus, where three toes have only a single metatarsal of remarkable 

 length terminating in three articular heads. The single metatarsal 

 of the Solidungula has only a single articular head, but two style- 

 shaped and very slender adjacent bones. Most of the remaining or- 

 ders have the number of toes from 3 to 4 ; the Quadrumana, Chei- 

 roptera, and most Carnivora, have 5. The number of toes is the 

 same as the ringers, only the great toe corresponding to the thumb is 

 frequently rudimentary, and has only one joint, or is wanting alto- 

 gether, while the remaining toes have generally three phalanges 

 each. In the Apes the metatarsal and phalangeal bones are much 

 slenderer than in Man. 



MUSCULAR SYSTEM. 



THE several orders and genera of Mammalia present the greatest 

 diversities in reference to the muscles of the extremities. In the 

 greater number of cases, especially as regards the higher orders, the 

 muscular system may be referred to the human type. While, how- 

 ever, the thin flat muscles which lie beneath, and serve to corrugate 

 the integument, are very slightly developed in Man, and are limited 

 to particular situations (M. frontales, occipitales, platysma-myoides, 

 &c.), they occur in the Mammalia as muscular layers spreading over 

 the whole face, shoulder, and abdomen. In many cases they coa- 

 lesce more or less together, and in those animals particularly which 

 can roll themselves up in a ball, they form a very large thick fleshy 

 lamina, which can be drawn like a cap over the whole back, sides, 

 and part of the extremities, e. g. in the Porcupine and Hedgehog, in 

 which last the tegumentary muscle is short, hood-shaped, very thick, 

 and separable into two layers. 



The muscular system of the Apes, even of the highest, exhibits 

 many departures from that of Man. The muscles of the extremities 

 are arranged according to a more analogous type. The individual 

 mobility of the fingers is much more limited in them than in 

 Man, and this is particularly the case with the thumb. The short 

 extensor of the thumb is wanting ; the flexor brevis is blended 

 with the adductor ; the flexor longus pollicis is not a distinct 

 muscle, but only a tendon of the flexor digitorum communis pro- 

 fundus ; the extensor longus pollicis forms a common muscle with 

 that of the index and middle fingers. The want of a distinct ex- 



