1926] Hall: Slvll of the Bodent Otospermophilus grammurus ieechei/i 391 



crown view than the permanent tooth. In the permanent tooth the 

 protocone is relatively higher and wider, and on the lingual sid© slopes 

 less abruptly downward than in the milk tooth. One of the most 

 striking differences lies in the anterior cingulum, which in the per- 

 manent tooth is lower than the paracone or metacone bnt in the milk 

 tooth is fully as high as either the paracone or metacone. In the per- 

 manent tooth the paracone is higher than the metacone ; in the milk 

 tooth the two are of about equal height. The metaconule is fully as 

 well, if not better, developed in the milk tooth than in the permanent 

 tooth. In the latter the ridge connecting the metaconule with the 

 metacone is better developed but the ridge connecting the metaconule 

 with tlie protocone is better developed in the milk tooth. The posterior 

 cingulum extends almost to the lateral margin of the milk tooth, but 

 in the permanent tooth terminates only a short distance beyond the 

 valley which separates the metacone and metaconule. The permanent 

 tooth is more molariform than the milk tooth. However, paradoxical 

 as it may seem, the milk tooth, when all things are considered, is more 

 complex than the permanent tooth. Other changes in the teeth that 

 occur with advancing age are due to wear. In very old individuals 

 the metaloph, paraloph, and loph of the anterior cingulum are very 

 broad and connect with the larger protoloph. 



Cranium as a Whole 



The foregoing discussion has dealt largely with individual bones 

 or components of the skull. Changes that occur in the skull as a whole 

 remain to be considered. It is obvious that any adequate comprehen- 

 sion of these changes involves constantly keeping in mind the changes 

 that occur in the component parts. 



Portions of the skull which the measurements given in table 2 show 

 to have increased three or more times between the two points from 

 which measurements were taken ara: length of nasals, 370 per cent; 

 l^ostpalatal length, 324; zygomatic breadth, 288; depth of skull at 

 center of palate between first premolars, 279 ; mastoid breadth, 270 ; 

 fronto-parietal length, 265 ; depth of skull at anterior border of basi- 

 occipital disregarding crest, 264; frontal length, 263; occipito-nasal 

 length, 250; condylo-basal length, 244; parieto-interparietal length 

 (not given in table 2), 244; diastema, 227; depth of skull at center 

 of palate near posterior margin of palatine bone, 214 ; least interorbital 

 breadth, 212 ; greatest width of nasals, 200. Measurements that show an 

 increase of less than three times, with the percentages of increase, are : 

 palatal length, 197 per cent ; maximum breadth of braincase at base 



