MYOLOGY 57 



fibers have deep origin from the diapophyses of the sacral 

 and caudal vertebrae. The long, slender tendons which 

 are developed from them pass to the dorsal part of the 

 caudal vertebrae farther caudad. 



M. abductor caudae externus (figs. 7, 12, 33) has 

 origin from the medial border of the pubis extending from 

 the symphysis to a point mediad of the acetabulum. It is 

 separated from its fellow of the opposite side by the urethra 

 and rectum. Insertion is upon the diapophyses of the 

 first five caudal vertebrae. 



M. abductor caudae internus (figs. 12, 33) has origin 

 along the medio-ventral border of the ilium from the 

 point of articulation with the sacrum caudad to the iliopec- 

 tineal eminence. It passes caudad partly mediad to the 

 abductor caudae externus, and tendons extending from it 

 join those of the flexor caudae muscle. 



The muscles of the tail are served by the coccygeal 

 branches of the spinal nerves, not followed in the present 

 instance. 



F. Perineal musculature 



Only four of these, exclusive of the sphincter ani internus 

 layer (p. 97) occur with sufficient distinctness to merit 

 recognition, and of these the external sphincter is the only 

 one common to the two sexes. There probably are ves- 

 tigeal fibers of other muscles, but if so their definition is 

 too poor for their inclusion in the present work to be justified. 



Mm. sphincter ani externus bulbocavernosus 



ischiocavernosus compressor urethrae 



M. sphincter ani externus (figs. 6, 21) occurs as a 

 thin muscle band surrounding the anus, and to all intents 

 it may be considered as an unpaired muscle. Insertion is 

 upon the body of the urethra in the male, and the cervix 

 uteri in the female. 



M. ischiocavernosus (figs. 21, 32, 33) in the male takes 



Ir^ 



