MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES OSGOOD. 25 



passes ectad over the scalenus from an origin on the superior transverse 

 process of the third cervical. This arrangement differs from that of 

 Didelphis in which the scalenus is entirely laterad of the serratus. In- 

 sertion on the posterior vertebral border of the scapula craniad of 

 the insertion of the serraius and continuous with it. 



Serratus posterior superior. Insertion by digitations from the 

 fourth to the ninth ribs inclusive. Dorsally it is mostly aponeurotic 

 but a broad fleshy prolongation extends anteriorly to the lower border of 

 the splenius, thence becoming aponeurotic as it crosses that muscle and 

 continues between the splenius and the rhomboideus to the most anterior 

 point of its origin on the nuchal crest above the sixth cervical spine. 

 Thence caudad its origin follows the mid-dorsal line and its wide apo- 

 neurosis covers the longissimus dorsi and continues into the lumbar 

 fascia. 



Serratus posterior inferior. Origin on the middorsal line with the 

 lumbar fascia. Insertion from the tenth to the thirteenth ribs. Practical- 

 ly as in Didelphis. 



Splenius. Origin from the nuchal crest from the vicinity of the 

 front of the axial spine to the second thoracic vertebra. Insertion on the 

 occipital crest from the mastoid process of the squamosal to a point 

 about 2 mm. from the median line. Its lower border is free as usual and 

 near its caudal extremity it is somewhat attached to the aponeurosis 

 of the serratus posterior superior. 



Biventer cervicis. Origin from the transverse processes of the fifth, 

 sixth, and seventh thoracic vertebrae. Insertion fleshy or very slightly 

 aponeurotic on the occiput between the median line and the complexus 

 to which its lateral border is attached for some 4 mm. Anteriorly it 

 reaches nearly to the parietal bones. It is a larger and thicker muscle 

 than in Didelphis and lies with its counterpart for a great part of its 

 length in the space between the elevated axial spine and the second 

 thoracic spine. 



Compkxus. Origin from the articular processes of and the aponeu- 

 rotic arches between the last six cervical and the first five thoracic 

 vertebrae. A large slip somewhat connected also with the longissimus 

 capitis runs forward to the transverse process of the atlas. Insertion 

 by a broad tendon on the occipital crest laterad of the biventer to within 

 about 3 mm. of the mastoid bulla. 



Longissimus capitis. Origin from the articular processes of the last 

 six cervical and the first four thoracic vertebrae in intimate relation 

 with the slips of origin of the complexus. Insertion by broad tendon on 

 the upper cranio-lateral border of the mastoid bulla and to a slight 

 extent on the adjoining part of the squamosal. 



