CHAPTER Vn. 



THE MtrSOLES AND THE VISCEEA OF THE SAUEOPSIDA. 



The most important deviations from the ordinary arrange- 

 ment of the muscular system occur, as might be expected, in 

 the Ophidia^ in the Chelonia, and in Aves. In the iirst-men- 

 tioned group, the numerous muscles of the limbs are, of course, 

 absent, and the mobility of the vertebrae, ribs, and jaws, is ac- 

 companied by a corresponding differentiation of the muscles 

 of those parts. The episkeletal muscles form a continuous 

 series (divisible into spinalis, semispinalis, longissimus dorsi, 

 levatores costarum, and other muscles) from the end of the tail 

 to the head ; and, in the region of the back, constitute a thick 

 mass which extends outward to the ends of the caudal ribs 

 (the so-called transverse processes), and over the dorsal thirds 

 of the other ribs. Beyond these points it is continued, as a 

 thinner layer of muscular fibres, over the ventral half of the 

 tail and trunk, passing from rib to rib in the latter region, 

 where the more dorsal fibres are directed obliquely, only a 

 longitudinal band running along the extremities of the ribs 

 and representing a rectus abdominis. This muscle is contin- 

 ued forward to the hyoidean apparatus, and thence to the 

 mandible. Superficial muscular bundles pass from the ribs to 

 the scales. The hyposkeletal muscles are better developed 

 than in most other Vertebrata, and also extend from the head 

 to the end of the tail. A median dorsal set are connected with 

 che subvertebral processes in the trunk, and with the bases of 

 the representatives of the chevron-bones in the tail, and pass 

 to the caudal and dorsal ribs. One set of these, in the trunk, 

 act as retractors of the ribs. The muscles which correspond 

 with the transversus abdominis commence in the tail by trans- 

 versely-directed bundles of fibres, which arise from the roots 

 of the caudal ribs (transverse processes), and meet in a median 



