26 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



The biventer, complexus, and longissimus capitis are well distinguished 

 from each other and in their general relations are as in Didelphis. At 

 least one distinct tendinous inscription crosses the anterior part of each 

 some 4 mm. from the insertion. 



Rectus capitis posterior superficialis. Origin from the crest of the 

 axial spine. Insertion entad of the complexus on the occipital crest. It 

 runs downward and forward with free upper and lower borders, leaving 

 a triangle on either side of the median line in which the much smaller 

 halves of the rectus minor and part of the rectus major are exposed. 



This muscle, often found in carnivores, is not generally reported for 

 marsupials, although Parsons (1896, p. 694) reports the rectus major 

 as bilaminar in Pelrogale. It is thin and flat and covers a great part of 

 the rectus capitis posterior major. In Didelphis, it is only partially 

 separable from the rectus major, in Marmosa it is somewhat freer, and 

 in Ccenolestes it is quite independent. 



Rectus capitis posterior major. Origin from the craniad surface of 

 the axial spine and intermuscular septa with the obliquus inferior. 

 Insertion on the occiput from the base of the paroccipital process dorsad 

 along the caudal border of the mastoid bulla to a point on the occipital 

 crest midway to the median line. It meets its fellow of the opposite 

 side in front of the axial spine and the two have tendinous connection 

 there and to a slight extent also with the caudal border of the neural 

 arch of the atlas. Its under surface has relation with the rectus capitis 

 posterior minor and with the surface of the neural arch of the atlas. It 

 is a rather thick muscle only slightly smaller than the obliquus inferior 

 with which its lower border is in apposition. 



Rectus capitis posterior minor. Origin from the straight anterior 

 border of the neural arch of the atlas. In a female specimen this meas- 

 ures 3 mm. in length from side to side. Insertion on the occipital from 

 a point near the median line nearly to the mastoid bulla. Its outer 

 surface has relation with the biventer, complexus, and rectus posterior 

 major. At the median line of the occiput it is separated from its counter- 

 part by i 2 mm. The two muscles approach each other and have 

 tendinous union in their caudal halves. 



Obliquus capitis superior. Origin from the lateral surface of the 

 transverse process of the atlas. Insertion tendinous on the occipital 

 ridge immediately dorsad of the mastoid bulla. A short flat muscle 

 crossing nearly at right angles to the large obliquus inferior and rectus 

 capitis posterior major which has relation with its inner surface. 



Obliquus capitis inferior. Origin from practically the whole lateral 

 surface of the axial spine. Insertion on the whole caudal surface of the 

 transverse process of the atlas. It is a thick heavy muscle running 



