1926] Hall: Skull of the Rodent Otospermophilus grammurus beecheyi 365 



by the orbitosphenoid. It is this part of the frontal that meets the 

 palatine bone. The contact is never much greater than it is in B where 

 it is first present. In fact, on the average, it becomes less, externally, 

 in progressively older skulls. On the right side of L a process of the 

 maxilla extends backward and meets the orbitosphenoid ; thus exclud- 

 ing contact of the frontal and palatine externally. This, however, is 

 the exception rather than the rule. Ventrally the two frontals are 

 separated only by the presphenoid and the thin wings of the orbito- 

 sphenoids and palatines that extend forward with the presphenoid. 

 The orbitosphenoids are first in contact with the frontals in E. In C 

 anterior portions of the alisphenoids become ossified and are in contact 

 Avith the frontals. The frontals are in contact with the lacrymals from 

 the time the latter first appear, which is in B. The development and 

 relation of the turbinals to the frontals and to the other elements con- 

 cerned chiefl}^ with the olfactory sense, were not made out in the 

 youngest skulls since to study these parts it would have been necessary 

 to disarticulate other elements which it was desirable to keep in place 

 for comparative study. In adults, however, the frontals' relation to 

 the turbinals was noted. Here the cribriform plate is supported by 

 the frontals along its entire border except for a narrow space ventrally 

 where it comes in contact with the presphenoid, and perhaps the vomer. 

 In three skulls examined the cribriform plate was situated on a trans- 

 verse plane of the skull that passed in front of the supraorbital notches 

 and through the last upper molars. Internally, the frontals bear ridges 

 and concavities that mark the position of the turbinal scrolls. Behind 

 the cribriform plate the olfactory lobes leave two depressions. Other- 

 wise, within the cranial cavity, the frontals bear but few impressions 

 left by blood vessels or other structures of the soft anatomy. It is 

 seen from table 2 that the least interorbital breadth of the frontals 

 increases 212 per cent. The ratios given for this measurement of the 

 series of skulls express the relations that exist in proportion between 

 this width and the occipito-nasal length. The largest ratios are in 

 B and D. The ratio grows less upward through the series until the 

 adults are reached at which place the ratio increases again. This last 

 increase represents the greater development of the orbital ridges in old 

 individuals. Another change due to very great age, which is present 

 in most skulls of Q, is the closure of the supraorbital notch that carries 

 branches of the anterior facial vein, internal ( ?) carotid artery, and 

 fifth (?) cranial nerve. In Q this notch has become changed into a 

 canal (see figs. 1-6), 



