THE CAT 267 



of the skull back of the orbits. The optic capsule does not ossify, 

 but a membrane bone, the lachrymal, appears at its anterior end. 

 The orbit, in which the eye lies, is formed of the bones of the 

 brain case and the visceral skeleton. The nasal capsules are bony 

 and cartilaginous, and form the forward end of the skull. 



The bones of the visceral skeleton fall readily into three cate- 

 gories, according to their position: those of the upper jaw and 

 upper part of the face, those of the lower jaw, and those of the 

 tongue. 



The Dorsal and Posterior Aspects. The hinder end of the skull 

 is formed of a single bone, the occipital, which has been formed 

 by the fusion of four bones: the ventral basi-occipital ; the two 

 exoccipitals, which bear the two occipital condyles ; and the dorsal 

 supra-occipital. 



In the dorsal aspect the small interparietal bone forms the 

 median portion of the lambdoidal ridge. In front of this ridge 

 are the large, paired parietal bones, and in front of these the large, 

 paired frontal and the paired nasal bones, the latter lying at the 

 anterior end of the skull. These bones are all membrane bones 

 and form the roof of the skull. 



Lateral to each parietal is the large temporal bone, which con- 

 tains the auditory organ. Projecting forward from it is the 

 large zygomatic process, which forms the hinder part of the 

 zygomatic arch. 



On each side of the nasals is the maxillary bone, and in front 

 of them are the two intermaxillary bones ; these two pairs of 

 bones bear the teeth. Projecting backward from the maxillary 

 on each side is its zygomatic process, which forms the anterior 

 portion of the zygomatic arch. The middle portion of the arch 

 is formed by the malar bone. Extending from this bone me- 

 dially and dorsally is its frontal process, which almost meets the 

 zygomatic process of the frontal bone and separates the orbit 

 from the temporal fossa. 



Between the maxillary and frontal bones in the orbit is the 

 small lachrymal bone. 



Exercise 57. Draw a view of the dorsal aspect of the skull, with 

 the outlines of the bones which appear. 



