130 ANATOMY OF THE WOOD RAT 



gressively much larger, until the width between their points 

 at the sixth may be as much as 17 mm. (in a very old indi- 

 vidual of Teonoma) . As suggested, their size increases much 

 with age. This sixth is the only vertebra of the lumbar 

 series in which there is practically no anapophysis. In none 

 of the vertebrae does a prezygapophysis occur as a true 

 process. 



Jayne (1898) designates the diapophyses as ''transverse 

 processes," which seems unfortunate, for they are not homol- 

 ogous with what he (and I) have termed the transverse 

 processes of the more cranial of the thoracic series. His 

 "manuTiillary process" and "accessory process" are also less 

 desirable terms than the corresponding metapophysis and 

 anapophysis. 



The definition of the ventral ridge or hypapophysis upon 

 the body of the lumbar vertebrae of Homodontomys increases 

 progressively from barely perceptible upon the first to very 

 sharp upon the sixth ; but this is the case to a lesser extent in 

 Neotoma and Teonoma. 



The multifidis spinae is situated between the spines and 

 the metapophyses, while the muscles most intimately con- 

 cerned with the diapophyses are the longissimus dorsi, 

 quadratus lumborum and psoas magnus. The psoas minor 

 and flexor caudae longus also have attachment upon these 

 vertebrae. 



Sacral vertebrae 



The four sacral vertebrae have a total length in Homo- 

 dontomys of 28.2, 23.5, and 22 mm., or 19.3, 17, and 16.7 

 per cent of the vertebral body length. In Neotoma these 

 figures are 20, 18.5, and 19 mm., or 18.3, 17.6, and 18 per cent. 

 In Teonoma they are 26.5 and 24 mm., or 18.2 and 17.5 

 per cent of the body length. 



In the case of the animals under discussion these vertebrae 



