MUSCULAR SYSTEM OF MAMMALIA. 5 



and extends from the dorsal aspect of the sacrum along the spine 

 to the third or fourth cervical vertebra. It is continued forward by 

 the transversalis cervicis and trachelo-mastoideus, which are blended 

 into a single oblong muscle arising from the anterior dorsal and 

 inserted into the transverse processes of the six lower cervical 

 vertebrae and the mastoid process. 



The sterno-mastoid is a double muscle on both sides, one por- 

 tion being superficial, 8, the other deep-seated ; each arises sepa- 

 rately from the episternum, and is separately inserted into the 

 mastoid. The omo-hyoideus, 10, and mylo-hyoideus, 10, have a 

 common insertion into the hyoid. A muscle, l", arising from 

 the basi-hyal and expanding to be inserted into the lower lip, 

 serves to retract this part. The stemo-hyoideus, n, joins the hyo- 

 ylossus. The genio-hyoideus, 12, and the stylo -hyoideus, 13, have 

 the normal relations : the biventer maxillce, H, is a short thick 

 muscle, inserted near the bend, representing the angle, of the jaw. 



The caudal muscles are powerfully developed. The oblique 

 fibres of the inferior or deflector muscles are shown at 53 ; they 

 are removed on the other side to expose the anterior caudal 

 nerves, i. The obliquus externus abdominis, 3, 3, arises from all 

 the vertebral ribs, except the first, and from the dilated ex- 

 tremity of the ilium ; it is inserted by a strong tendon into the 

 outer extremity of the marsupial bone, vi, then expands into an 

 aponeurosis which is attached to the internal margin and base of 

 that bone, and into the symphysis pubis, decussating with the 

 tendinous fibres of the opposite muscle : it does not split to form 

 an ' abdominal ring.' 



The obliquus internus, 6, arises from the anterior part of the 

 ilium, expands, and is inserted into the broad cartilages of the 

 seven posterior ribs, v, v. 



The transversus abdominis, 7, is a thicker muscle, and arises 

 from both the ilium and the lumbar diapophyses ; its tendon 

 passes behind the recti to blend with that of the opposite muscle, 

 and with the aponeurosis of the obliqui externi, in the linea alba. 



The pyramidalis, or superficial rectus, 4, is here, as in the 

 ordinary Marsupials, of very large size ; it arises from the whole 

 inner margin of the marsupial bone ; its fibres converge toward 

 and are confluent at the linea alba with those of its fellow, and it 

 gradually terminates in a point opposite the posterior part of the 

 sternum. It depresses the ribs, shortens the abdomen, and pro- 

 tracts the marsupial bone. 



The rectus abdominis, or posterior rectus, 5, arises from the 

 posterior margin of the marsupial bone, and is inserted into the 



