MUSCULAR SYSTEM. 157 



versus abdominis (20,) extends over a large portion of the 

 trunk from the want of ribs in these anurous amphibia. 

 The inter-transversales (21.) are of considerable breadth, 

 from the length of the transverse processes of the vertebrae. 

 The pectoralis major, here of great size and strength, is 

 divided into several distinct parts, which extend forwards, 

 inwards, and backwards, as separate flat muscular bands, 

 covering a great portion of the anterior surface of the trunk. 

 The muscles of the os hyoides are of great size, as in fishes 

 and the lower amphibia, from the size of that bone, and its 

 importance in respiration where there are no ribs. The pec- 

 toralis minor is also divided into several detached and di- 

 verging muscular bands, like the external, arid both these 

 muscles acquire increased influence on the arm by their low 

 insertion on the short humerus. The deltoid (7,) the anco- 

 nei (9, 10,) and most of the proximal muscles of the arm are 

 strong ventricose masses, and even the flexors and extensors 

 of the wrist and fingers are short and fleshy, giving an an- 

 thropoid character to these members. The knees extend, 

 not forwards as in most vertebrata, but directly outwards 

 from the sides of the trunk, and the long webbed feet have 

 the same lateral direction, the best adapted for swimming 

 and leaping. The glutei muscles (27,) are here long and 

 narrow, from the lengthened and cylindrical form of the iliac 

 bones, and also the iliaci muscles (28, 37,) and the semi- 

 tendinosus (33,) the semi-membranosus (31,) and other ex- 

 tensors of the thigh. The recti (29,) and the vasti muscles 

 (40,) and the other extensors of the knee-joint, and also the 

 gastrocnemius (34,) the tibialis posticus (42,) the peronei (48,) 

 and other extensor muscles of the heel are here of great size, 

 and of great importance in the progressive motions of these 

 animals both on land and in the water, and by their great 

 development they give a rotundity to the thighs and to the 

 calfs, unusual in the cold-blooded vertebrata. The plantar 

 aponeurosis is here continued from the tendo achilles, which 

 has a moveable sesamoid bone where it plays over the heel ; 

 so that the great extensors of the heel-joint contribute like- 

 wise to the flexion of the toes, and the general support of 

 the long webbed feet in swimming through the water, or in 

 leaping on the ground. 



The higher classes of air-breathing vertebrata, by respiring 



