132 ANATOMY OF THE WOOD RAT 



vertebrae in one, and probably 25 in the other. Of the lat- 

 ter, the tail is slightly damaged, and it is believed that but 

 one vertebra is missing. In two specim.ens of Homodon- 

 tomys the caudal series measures 196 and 215 nun., or 134 and 

 156 per cent of the vertebral body length. In Neotoma 

 these figures are 148, 130, and 137 mm., or 136, 124, and 

 129 per cent of the body. In Teonoma the measurements 

 are 175 and 166 mm., or both 119 per cent of the body 

 length. These vertebrae are most robust in Homodontomys 

 and lightest in Neotoma, conforming to expectations in con- 

 sideration of different life habits. 



It is individually variable whether the first two or first 

 three caudal vertebrae are the only ones of this series whose 

 spines extend farther dorsad than the other processes. These 

 decrease in height progressively in caudal sequence. Simi- 

 larly with the diapophyses, which are a trifle the largest in 

 Homodontomys and smallest in Neotoma. Those of the first 

 caudal are practically as broad as in the sacrals, but in each 

 succeeding vertebra they are smaller. In the fifth they are 

 very small, and in Homodontomys only there is situated 

 directly caudad to them a pair of miniature replicas. The 

 anapophyses are also well developed in the first five verte- 

 brae, being successively and progressively smaller caudad. 

 In reality transition from the first caudal vertebra to the 

 form typical of those of the middle tail is quite gradual; 

 but it can be said that the first five are of the proximal type, 

 and the remainder of the distal. Each of the latter has a pair 

 of metapophyses in the form of tubercles, a mid-dorsal ridge 

 terminating caudad in a pair of small postzygapophyses 

 that are practically coalesced, a lateral ridge upon either 

 side that consists of modified di- and anapophyses, and 

 ventrad, a pair of hypapophyses which are prolonged caudad 

 to form a single mid-ventral ridge. Chevron bones occur 

 caudad at least to within six vertebrae of the tail tip. No 

 definite statement in regard to their number can be ventured, 



