MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 27 



downward and forward. In Didelphis, this muscle extends to the 

 third, fourth and fifth cervical spines, but in Marmosa it is much as in 

 C&nolestes. 



Rectus capitis anticus major. Origin on the transverse processes of 

 the last five cervical vertebrae. Insertion on the posterior third of the 

 basisphenoid and the anterior two fifths of the basioccipital slightly 

 laterad of the median line. Some of its superficial fibers extend caudad 

 with the longus colli to the ventral side of the posterior thoracic verte- 

 brae. Anteriorly it forms a good sized bundle and is not peculiar except 

 for the extent of its attachment to the basisphenoid which is more than 

 usual. 



Rectus capitis anticus minor. Origin on the middle third of the ven- 

 tral surface of the neural arch of the atlas midway between the median 

 tubercle and the transverse process. Insertion on the ventral surface 

 of the basioccipital in its anterior lateral fourth. A thin flat muscle 

 lying entad of the rectus anticus major and mediad of the rectus capitis 

 lateralis but entirely free from both. 



Rectus capitis lateralis. Origin on the transverse process of the atlas. 

 Insertion slightly tendinous on the outer edge of the basioccipital along 

 the carotid canal and thence forward to the basisphenoid and by tendi- 

 nous fascia to the presphenoid. Certain lateral fibers attach on the 

 periotic. It is a well developed muscle and entirely distinct, extending 

 farther cephalad than in Didelphis. 



Longus colli. The dorsal part of the longus colli is rather distinct, 

 extending from the transverse process of the sixth cervical along the 

 bases of the ribs and the sides of the vertebrae to the fourth dorsal 

 vertebra. Between its two halves are fibers which extend into the 

 cervical part but they are lateral in position and the median ventral 

 surfaces of the dorsal vertebrae are mostly covered only with tendinous 

 fascia. The cervical part consists of various converging slips from the 

 transverse processes of the cervical vertebrae and caudally from the 

 sides of the ventral surfaces of the vertebrae. Over the atlas it shows six 

 rather distinct divisions, two medial ones inserting on the tubercle of the 

 atlas and two on either side inserting on the body. 



Spinalis dorsi.The spinalis dorsi disengages from the medial side 

 of the longissimus about opposite the eighth thoracic vertebra, the cau- 

 dal part of the biventer cervicis forming a wedge between the two. Its 

 inner fibers run to the spines of the anterior thoracic vertebrae but its 

 lateral fibers form a practically distinct subvertical ribbon which runs 

 forward and inserts on the side of the low spines and bodies of the fourth 

 to the seventh cervicals and the first thoracic. It passes the high spine 

 of the second thoracic without definite attachment, but between the 



