viii. 1 THE MUSCLES. 333 



the Hedgehog, and Pig), or there may be but one, as in 

 Pteropus. The thumb, on the contrary, may have its own 

 lumbricalis, as in Dasypus Sexcinctiis^ and there may be 

 eight in the hand, as in Galeopithecus. 



The pronator quadratiis may be much more elongated 

 than in man, as in the Dog and Cat. It may, however, be 

 completely wanting, as in the Flying Fox and in the Horse. 

 An accessory pronator may be developed (as in the Iguana 

 and Chameleon), arising from the internal condyle and radial 

 border of the ulna, and being inserted into the lower part of 

 the radius between the insertions of the pronator teres and 

 pronator quadratus. 



FIG 301. DEEP FLEXOR MUSCLES OF FORE-ARM OF Iguana, the more superficial 



ones being cut and reflected. 

 B, biceps ; FCR, flexor carpi radialis ; FCU, flexor carpi ulnaris ; FPD, flexor 



profundus digitorum ; PA, pronator accessorius ; PQ, pronator quadratus; 



PT, pronator teres ; SA, supinator accessorius; SL, supinator longus. 



Supinator longns. This is a very inconstant muscle, as 

 might be expected from its action, which is related to the 

 exceptional mobility of the fore-arm and hand of man. Thus 

 it is totally absent in many animals, e.g. the Horse. It may, 

 on the contrary, attain a vastly greater relative size than in 

 man, as in Bradyp^ls, where it takes origin from the lower 

 three quarters of the humerus, and is separable into two 

 parts ; it is large and double in some Reptiles, e.g. the Iguana 

 and Chameleon (Figs. 302 and 303). 



The extensor carpi radialis longior is exceptionally distinct 

 in man, for in most Mammals it is more or altogether united 

 with the extensor carpi radialis brevior. 



