THE SKELETON 



39 



aperture. The orbits appear almost circular in shape in this 

 view while the nasal aperture is median and heart-shaped. 



Bones of the Disarticulated Skull. — The skull is usually con- 

 sidered in two parts, the cranium and the face. The former is 

 composed of nine bones which will be described in order. 



The frontal hones (Figs. i6 and 17) are two in number, 

 lying between the orbits, and articulating with one another 



haricl-cd 





\ Yonti 



p-niy. rna^z llat^y ?> 



^1"^ 



Fig. 16. — Diagram of the Bones of the Mammalian Skull Viewed 



Laterally. 

 I, 2, 3, etc., indicate the places of exit of the twelve cranial nerves, pmx, 

 Premaxillary; ty, tympanic, 7 and 8 are on periotic; thy, tympanophyal; shy, 

 stylohyal; ehy, epihyal; chy, ceratohyal; hhy, basihyal; thhy, thyrohyal. The car- 

 tilage bones are shaded. {From Flower, after Huxley.) 



in the median line. They form the roof of the cranial part 

 of the brain cavity and the caudal portion of the roof of the 

 nasal chamber. A lateral projection {po, Fig. 17) is known 

 as the postorbital process. Within the frontal bone is a cavity, 

 the frontal sinus (Fig. 19), which contains air and is lined with 

 mucous membrane. It communicates with the nasal cavity. 

 The lateral descending portion of the bone, articulating with 



