192(5] Hall: Slull of the Fodcni OtoftpermophUns grammurus heccliejii Sfio 



the frontals in this case. Near the median line of the skull, however, 

 the relation of these two bones is reversed, and the frontal overlaps 

 the parietal to a distance of 1.3 mm. It is interesting to note that the 

 place where the parietal overlaps the frontal is the place where the 

 parietal and frontal first come into contact and that the place where 

 the frontal overlaps the parietal is the place where the parietal and 

 frontal last come into contact. This portion of the parietal that over- 

 laps the frontal reaches the postorbital process in G. 



The supraorbital ridges gradually rise and in M project above the 

 rest of the dorsal surface of the frontals. The ridges also increase in 

 thickness and become very heavy in Q. Externally, between the orbits, 

 the frontals are convex from A to K. Externally, they are also convex 

 longitudinally from .4 to F. This longitudinal convexity is most pro- 

 nounced in A and B where the frontals dip sharply downward to meet 

 the nasals. This is perhaps partly the result of the relatively greater 

 development, in these stages, of the brain than of the structures housed 

 by the preorbital portion of the skull. The entire frontal suture is 

 present in L and the anterior part of this suture in M to P, but in Q 

 it can not be made out, the frontals having fused throughout their 

 entire length. 



The frontals are in contact with the following bones : nasals, pre- 

 maxillae, maxillae, palatines, presphenoid, lacrymals, orbitosphenoids, 

 alisphenoids, squamosals, parietals, and ethmoids. It has already been 

 pointed out that the nasals come into contact with the frontals in B 

 and later overlap the frontals, also that the premaxillae come into 

 contact with the frontals in C and that the maxillae reach across the 

 fontanelles that persist immediately in front of the lacrymal regions 

 in H and at this time come in contact with the frontals at this point. 

 Within the orbits, however, ossified parts of the frontals and maxillae 

 reach one another in B. Within the orbit the frontal reaches the 

 maxilla along most of the anterior half of their contact but the 

 maxilla overlaps the frontal along the posterior half of their contact. 

 The two wings of the premaxillae that lie alongside the nasals, like 

 the nasals also overlap the frontals, but between each premaxillary 

 wing and each nasal a process of the frontal, 2 or 3 mm. long, lies at 

 the dorsal surface of the skull and slightly overlaps the lateral border 

 of the premaxilla. The contact of the frontals with the palatines is 

 made in B. On each side in B and in C there is present what appears 

 to be a separate center of ossification, namely, the region of the part 

 of the frontal that lies immediately anterior to the region later occupied 



