THE SKULL 45 



b Membrane-bones of cranium. 



i. The frontoparietals are two long flat t>ones on the 

 top of the brain-case, covering the fontanelles, and 

 overlapping the hinder end of the sphenethmoid. 

 ii. The parasphenoid is a j_-shaped bone on the ventral 

 surface of the cranium ; its lateral processes 

 underlying the auditory capsules. 



2. The Sense Capsules are cartilaginous and bony capsules 

 which surround and protect the olfactory, optic, and 

 auditory organs; two of them are fused with the 

 cranium so as to form parts of the skull. 

 a The auditory capsules are fused with the sides of the 

 posterior end of the cranium, to which they form 

 wing-like projections : they consist largely of cartilage. 

 i. Cartilage-bone of auditory capsules. 



The pro-otics are a pair of irregular-shaped bones 

 in the anterior walls of the capsules, and forming 

 also parts of their roof and floor. 



b. The optic capsules are not fused with the skull. They 

 remain permanently cartilaginous under the name of 

 the sclerotic cartilages of the eyes. 



C. The olfactory capsules are fused with the anterior end 

 of the cranium, and also with each other. They 

 consist very largely of cartilage, which is produced in 

 front into the rhinal processes. 



i. Cartilage-bone of olfactory capsules. The spheneth- 

 moid, as already noticed, extends forwards so as to 

 invade the olfactory region, but does not properly 

 belong to the olfactory capsules. 

 ii. Membrane-bones of olfactory capsules. 



a. The nasals are two triangular bones on the dorsal 

 surface of the anterior end of the head : the bases 

 of the triangles are turned towards the middle 

 line and meet each other in front, while their 

 posterior ends diverge and enclose, with the 

 anterior ends of the frontoparietals, a diamond- 

 shaped patch in which the sphenethmoid is visible 

 on the dorsal surface of the skull. 

 ft. The vomers are two tri radiate bones on the ventral 

 surface of the fore part of the skull : each vomer 

 bears in its inner or posterior angle a small 



