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CHAPTER VII. 



THE MUSCLES AND THE VISCEKA OF THE SATJEOPSIDA. 



The most importaiit deviations from the ordinary ar- 

 rangement of the muscular system occur, as might be 

 expected, in the Opliidia, in the Chelonia, and in Aves. In 

 the first-mentioned group, the numerous mxiscles of the 

 limbs are, of course, absent, and the mobility of the 

 vertebrae, ribs and jaws, is accompanied by a con-e- 

 sponding differentiation of the muscles of those parts. 

 The episkeletal muscles form a continuous series (divis- 

 ible into spinalis, semispinalis, longissimus dorsi, levatores 

 costm-um, 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 outwards to the ends of the caudal ribs 

 (the so-caUed 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 haK of the 

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

 where the more dorsal fibres are directed obliqviely, only a 

 longitudinal band running along the extremities of the ribs 

 and representing arecii«s abdominis. This muscle is continued 

 forwards to the hyoidean apparatus, and thence to the man- 

 dible. Superficial muscular bundles pass from the ribs to 

 the scales. The hyposkeletal muscles are better developed 

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

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

 the 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 



