278 SKELETON OF THE BABBIT 



process, which is placed nearly transversely 

 to the longitudinal axis of the skull,' and is 

 connected along its inner edge with the pala- 

 tine bone : it is perforated at its base by three 

 foramina, of which the innermost and largest 

 transmits the internal maxillary artery and 

 vein, and the two outer ones, branches of the 

 mandibular division of the fifth nerve. 



Between the ali-sphenoid and the anterior 

 end of the basi-sphenoid on each side is a 

 large slit-like notch, the sphenoidal fissure or 

 foramen lacerum anterius, through which the 

 third, fourth, and sixth nerves, and the first 

 and second divisions of the fifth pass out from 

 the cranial cavity into the orbit. 



At the posterior border of each ali-sphenoid 

 is a deep notch for the passage of the third 

 division of the fifth nerve. 



iii. The parietals are a pair of flattened mem- 

 brane-bones, articulating with each other in 

 the mid-dorsal line at the sagittal suture, and 

 forming a great part of the roof of the cranial 

 cavity. 



From the posterior and outer angle of each 

 parietal a thin plate runs down on the inner 

 surface of the squamosal, which latter bone 

 separates the parietal from the ali-sphenoid. 



iv. The interparietal is a small median bone in the 

 roof of the skuU, between the parietals and 

 the supra-occipital. 



0. The frontal segment surrounds the anterior end of 

 the brain : it is placed in front of the parietal 

 segment, with which it articulates closely, 

 i. The pre-sphenoid is a median, laterally compressed 

 bone in front of the basi-sphenoid, and con- 

 nected with it by cartilage. It forms the 

 lower margin of the optic foramen, a large 



