1926] Hall: Skull of the Rodent Otospermophilus grammurus heeeheiji 373 



anterius but a small canal external to it." This statement certainly 

 does not appl}^ to Jfannata, and, although Gregory (1910. p. 329) 

 lists Arctomijs [=--Marmota] as one of the genera in wliieli the 

 cranial foramina, at least, were examined by him, he makes no 

 mention of its being an exception to his general statement regarding 

 the alisphenoid canal. 



Palatines. — In A the palatines are separated from each other and 

 from the maxillae anteriorly by tracts of unossified cartilage. Each 

 pterygo-alisphenoid ridge is represented largely by a palatine at 

 this stage. The term pterygo-alisphenoid ridge is non-descriptive in 

 the case of Otospermophilus because the elements comprising it are 

 almost entirely the palatines and alisphenoids. Also, in Otospermo- 

 philus, this ridge is more plate-like than ridge-like. Viewed laterally 

 it is square in young skulls, but this shape changes with age until in 

 Q it becomes oblong, being narrower anteriorly than posteriorly. It 

 is also modified in older stages by the development on it of the 

 pterygoid fossa. A median ridge that is continuous with, and con- 

 temporaneous in time of development with, the median ridge men- 

 tioned in connection with the maxillae, develops on the palatines. 

 One of the most striking changes in the palatines is in the shape and 

 extent of the palatal spine (see figs. 15-20). In the embryo skulls, 

 A and B, this posterior margin of the palatines lies flat on the basi- 

 sphenoid, but in C the posterior margin of the palatines is raised 

 slightly above the basisphenoid. This margin continues to rise 

 throughout the series and in Q lies about 3 mm. above the basisphenoid. 

 In addition to the maxillae, orbitosphenoids, and alisphenoids with 

 which the palatines are in contact, they also support the pterygoids, 

 basisphenoid, and presphenoid. The palatines extend anteriorly to 

 the forward end of the presphenoid. However, except on the posterior 

 half of the basisphenoid, a narrow slit on either side of the pre- 

 sphenoid and basisphenoid separates them from the palatines. These 

 slits are never wide and in Q, at most points, become entirely closed. 

 The support given the basisphenoid by the palatines is accomplished 

 by their connection with the posterior half of each lateral border of 

 the basisphenoid and by a slight contact of the palatines with the 

 orbitosphenoids which in turn are in contact with the presphenoid. 

 In measuring the palatines (exclusive of the palatal spine) it becomes 

 evident that they are extremely variable in length in skulls of the 

 same age ; far more so than are the maxillae or premaxillae. In 

 Otospennophilus gnnnmunis heeeheyi, at least, a less variable meas- 



