60 VERTEBRATE ZOOLOGY 



skull and the medial walls of the orbits. Immediately back of 

 the frontal bone on each side is the small, irregular parietal, also 

 a membrane bone. 



The auditory capsule is formed of an intricate complex of bones 

 at the posterolateral corner of the skull. From the hinder end 

 of the capsule two prominent spinelike processes project, these 

 processes on the two sides, together with the median supra-occipital 

 spine, forming the five prominent projections at the hinder end of 

 the skull. 



Of the two lateral processes the more dorsal is the epiotic 

 process ; it is formed by the small epiotic bone, which lies lateral 

 to the supra-occipital and behind the parietal. The more ventral 

 process is the parotic process. It is formed by two bones, the more 

 dorsal being the pterotic, the more ventral the opisthotic ; the latter 

 contains the foramen of the glossopharyngeal nerve. Directly in 

 front of the opisthotic is the prootic bone, through the anterior 

 border of which go the trigeminal and facial nerves, and directly 

 above which is the sphenotic. These five otic bones are all carti- 

 lage bones which form the auditory capsule. 



Just in front of the prootic and sphenotic are two cartilage 

 bones, the orbitosphenoid and the alisphenoid, the former being 

 the more ventral of the two ; they belong to the cranium proper, 

 for they lie in the lateral wall of the brain case, and are not seen 

 from above. 



Anterior to the frontals and forming the anterior end of the 

 cranium are the paired nasals, which form the roof of the nasal 

 capsule. 



Exercise 34. Draw the dorsal aspect of the cranium on a scale of 2. 



Study the ventral aspect. Three bones form the medial por- 

 tion of the ventral wall of the cranium,— the basi-occipital at the 

 hinder end, the vomer at the forward end, and the long slender 

 parasphenoid, or parabasal, between. The latter two are membrane 

 bones; the vomer bears teeth and forms the ventral wall of the 

 nasal capsule. 



In front of the orbits and directly above the vomer are the 

 median ethmoid and the two lateral ethmoids, which are cartilage 



