MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 29 



point from the longissimus dorsi. The longissimus dorsi separates from 

 the spinalis dorsi about opposite the eighth thoracic vertebra and passes 

 cranio-ventrad between the iliocostalis and the biventer and longissimus 

 capitis from which it is entirely distinct. Its insertion is just caudad 

 of that of the longissimus cervicis on the transverse process of the fifth 

 and possibly also the fourth cervical vertebra. Its origin is from the 

 lumbar tendinous sheet from which it becomes fleshy in the vicinity of 

 the second lumbar vertebra. Passing forward it is conjoined with the 

 spinalis and consists of slips from the transverse processes of the 

 vertebrae. 



Iliocostalis. An anterior division or iliocostalis dorsi and a posterior 

 or iliocostalis lumborum are fairly distinct. The iliocostalis dorsi arises 

 by slips from the sides of the ribs from the first to the eighth. It passes 

 cranio-ventrad on the side of the neck laterad of the longissimus and 

 inserts on the superior transverse processes of the sixth and seventh 

 cervical vertebrae. For a short distance just before its insertion it is 

 merged with the longissimus. 



The iliocostalis lumborum arises from the complicated lumbar ten- 

 dons of the sacrospinalis and becomes fleshy opposite the fourth lumbar 

 vertebra. It inserts by thin flat slips on the sides of the ribs from the 

 sixth to the thirteenth. Between the ilium and the ribs it forms the 

 anterior lateral boundary of the mass of muscle filling the space between 

 the articular and transverse processes of the lumbar vertebrae. Over the 

 ribs it is thin and the slips are fairly distinct from each other. Between 

 the sixth and the ninth ribs it overlaps the iliocostalis dorsi which only 

 reaches the eighth rib. 



Sacrospinalis. Origin from the crest and the ventro-medial surface 

 of the cranial fourth of the ilium, meeting the origin of the iliacus, and 

 from the tendinous lumbo-dorsal fascia. Insertion on the dorsal surfaces 

 and caudal edges of the transverse processes of the lumbar vertebrae 

 and the twelfth and thirteenth dorsals. A thick rounded bundle ex- 

 tending from the ilium to the ribs. Easily separable from the multifidae 

 which lie mediad of it but covered by the tendinous fascia. It fills the 

 space on the side of the vertebral column between the articular and the 

 transverse processes of the lumbar vertebrae. 



Quadratus lumborum. Origin from the bodies of the i2th and i3th 

 dorsal vertebrae and the lumbar vertebrae from the first to the fourth. 

 Insertion on the tips and ventral surfaces of the transverse processes of 

 all the lumbar vertebrae except the last. It lies somewhat flattened 

 between the psoas parvus and the large rounded sacrospinalis and con- 

 nects the series of transverse processes with each other by series of 

 overlying tendons, the fibers from the under side of one running to the 



