28 FIELD MUSEUM or NATURAL HISTORY ZOOLOGY, VOL. XIV. 



first thoracic and the tip of the spine of the second it is traversed by a 

 strong tendinous inscription which may be partially attached to either 

 or both of the vertebrae. Anteriorly it passes between the lateral division 

 of the semispinalis cervicis and the long interspinal which connects the 

 spines of the fifth cervical and the second thoracic. In the opossum the 

 spinalis inserts as high up as the third cervical and the outer surface of 

 its anterior part is wholly in relation with the complexus. 



Semispinalis cervicis. In the region between the axial spine and the 

 second thoracic spine are two paired muscles which run ventrad toward 

 each other and meet at an angle over the sixth and seventh cervicals, 

 the posterior one passing inside the spinalis between the two halves 

 of the anterior one. The anterior of these muscles has been regarded 

 as the semispinalis cervicis. It arises on the bodies of the first thoracic 

 and the fifth, sixth and seventh cervical vertebrae and converges to insert 

 on the tip and side of the axial spine in opposition to the obliquus 

 capitis inferior. Its outer surface has relation with the complexus and 

 its inner with the spinalis. It is not apparent in Didelphis, but is present 

 in Marmosa. The posterior paired muscle, above-mentioned, which is 

 in the nature of an interspinal, may be described here also. Its origin 

 is on the side of the spine of the fifth cervical and its insertion on the 

 front of the tip of the spine of the second thoracic vertebra. It stretches 

 directly between these spines without connection with the intervening 

 vertebrae. Between its two halves the ligamentum nuchae passes to the 

 vertebral spines. Beneath its caudal part, but distinct from it, a paired 

 intervertebral connects the spines of the first and second thoracic 

 vertebrae,. Its outer surface has relation with the biventer and the 

 spinalis, its inner with the ligamentum nuchae. A corresponding muscle 

 is found in the opossum running to the sides of the thickened third 

 cervical spine, its two sides therefore being widely apart and, although its 

 actual relations are much as in Canolestes, its appearance is quite 

 different. In Marmosa the third, fourth and fifth cervical spines are not 

 enlarged as in Didelphis,. Consequently the arrangement of the neck 

 muscles is more nearly as in C&nolestes and many other marsupials. 



Longissimus. Anteriorly this is divisible into longissimus dorsi and 

 longissimus cervicis. Superficially the two divisions appear as one 

 muscle but the outer part which continues caudad may be partially 

 separated from an inner mostly concealed part which only extends cau- 

 dad to the fifth thoracic vertebra and which may be regarded as the 

 longissimus cervicis. It arises by slips from the laminae of the cervicals 

 and from the transverse processes of the thoracic vertebrae from the 

 first to the fifth. It inserts on the transverse processes of the cervical 

 vertebrae from the second to the fourth or fifth, being inseparable at this 



