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



In the character of the first thoracic and essentially in other respects, 

 the thoracic series of vertebrae, like the cervical, resembles that of 

 Perameles more closely than that of any other marsupial. It differs 

 chiefly in the last three thoracics which in Perameles have relatively high 

 spines and prominent mammillary processes. 



LUMBAR VERTEBRAE. 

 Plate XIII, Figs. 1-2. 



The six lumbars have no important peculiarities. The first three 

 increase slightly in size caudad but aside from the appearance of small 

 inferior anterior transverse processes they scarcely differ from the last 

 thoracic. There are still small accessory processes (anapophyses), the 

 spinous processes are low and ridgelike and the mammillary processes 

 (metapophyses) scarcely protrude beyond the articular surfaces of the 

 zygapophyses. The fourth lumbar retains the ridgelike spinous process, 

 but the transverse process, directed downward and forward, is con- 

 siderably increased in size. The fifth and sixth lumbars are somewhat 

 differentiated from the others. The transverse processes are longer, the 

 spinous processes, which are directed forward, are higher and more 

 hooklike, and the postzygapophyses are nearer together and turned 

 slightly upward. There are no accessory processes but the mammillary 

 processes are more prominent than in preceding vertebrae and the 

 laminae of the arch are compressed posteriorly for a narrowing neural 

 canal. The ventral surfaces of the bodies of the lumbars are slightly 

 differentiated posteriorly into two slight ridges or tubercles for the 

 psoas muscles. A single median ridge or a long hypapophysis is found 

 in various forms, in Phascologale, Antechinomys, Perameles and to some 

 degree in Marmosa. Double ridges on the posterior half of the body of 

 the vertebra similar to those in Ccenolestes have been observed in 

 Didelphis, Dasyurus, and Petaurus. 



The lumbar series as a whole may perhaps be said to be characterized 

 by the low and inconspicuous condition of the vertebral processes which 

 in most other forms are more highly developed. In this respect there is 

 some resemblance to immature specimens of Didelphis, but even in these 

 the anterior and posterior zygapophyses are connected by a sharp ridge 

 and the accessory processes are broad, heavy, and blunt instead of small 

 and pointed. 



SACRAL AND CAUDAL VERTEBRAE. 



Plate XIV. 



Two vertebrae have been regarded as sacral, although the second 

 touches the ileum only at the anterior extremity of its transverse process. 



