136 



COMPARATIVE MORPHOLOGY OF VERTEBRATES 



cle extends, ventral to the rectus, from the inner side of the marsupial 

 bones to the sternum, but disappears with the marsupial bones. 



The dorsal muscles are more conservative, undergo less modifica- 

 tion than those just mentioned, and always show, more or less 

 clearly, their metameric nature. They become connected with 

 various parts of the vertebrae and with the ribs, and are correspond- 

 ingly divided into different groups. Thus the spinales connect the 

 spinous processes, the transversales the transverse processes of the 

 successive vertebrae, while the transverso-spinales extend from the 

 transverse process of one vertebra to the spinous process of the next. 



my 



Fig. 146. — Budding of muscles of appendage from myotomes in Pristiurus, after Rabl. 

 b, muscle buds: tny, myotomes. 



In the higher vertebrates the anterior spinalis, connecting the first 

 vertebra with the skull, is divided into several rectus capitis muscles. 

 The longissimus dorsi group extends from the pelvis to the head, 

 lying on either side in the angle between spinous and transverse proc- 

 esses. It may be differentiated into separate muscles — a longis- 

 simus dorsi proper in the lumbar region, an ileo-costalis inserted on 

 the dorsal part of the ribs, and a longissimus capitis along the side of 

 the neck to the temporal region of the skull. 



The muscles which move the appendages are divided into the 

 intrinsic, which are located in the limb itself and have their origin 

 either from the bones of the limb or from the supporting girdle, and 

 the extrinsic, which have their origin on the trunk and are inserted on 

 the girdle or the base of the limb. The latter move the limb as a 

 whole, while the intrinsic bend the limb on itself. As would be ex- 

 pected from the motions of the fins, the intrinsic muscles are hardly 

 noticeable in the fishes, the various movements being accomplished 

 by the extrinsic group. These latter are divided into prfltractOTS 

 whiqji4rawthe member f orwar d ; reta;a ctors wh ich pull it back against 

 i^y; le vators w hich lift it and depressors which pull it down. 



the. 



