OSTEOLOGY 129 



The muscles more intimately concerned with the thoracic 

 series of vertebrae are the longus colli, bi venter cervices, 

 longissimus cervicis and dorsi, quadratus lumborum, trans- 

 versospinales, and possibly the complexus. A reason was 

 especially sought for the great length of the spine of the 

 second thoracic — a character found in many rodents — but 

 without success. The rhomboideus posticus originates 

 chieflj'' from this spine, being the only muscle which does so; 

 but in the opinion of the writer this is hardly sufficient to 

 a.ccount fully for its development. Similarly, no convincing 

 muscular reason was encountered for the change in form of 

 the lateral processes upon the more caudal vertebrae of the 

 thoracic series. As previously indicated, the interrelation- 

 ship of the muscle fibers of the long system are often so 

 extremely complex and difficult of precise definition that one 

 is inclined to be conservative in arriving at conclusions. 



Lumbar vertebrae 



Six lumbar vertebrae are found in the genus Neotoma. In 

 Homodontomys the series measures 46 mm. in all three speci- 

 mens, or 31.5, 33.3, and 35 per cent of the vertebral body 

 length. In Neotoma these figures are 35.3, 33, and 32 mm., 

 or 32.4, 31.3, and 30.3 per cent of the body length. In 

 Teonoma they are 45 and 44 mm., or 30.6 and 32.1 per cent 

 of the body length. 



In most respects the lumbars are very similar to the last 

 thoracic vertebrae — in processes and the spine — but each 

 grows successively larger than the one cranially preceding. 

 In Homodontomys the postzygapophyses of the last, and in 

 Neotoma and Teonoma of the last two, are appreciably 

 smaller than of the others. Upon the first lumbar vertebra 

 a small diapophysis is first found (see fig. 27). The trans- 

 verse mdth between the terminations of these processes is 

 about 7 mm. In each lumbar succeeding, these are pro- 



