THE SKELETON. 



nasal cavities removed, and the third should be cut trans- 

 versely on a line joining the middle of the orbits. The_ 

 ethmoid is usually visible externally as a small rhomboid 

 plate on the medial wall of the orbit between the frontal, 



barichd [w*^ 

 A I MES 



f-m^ *upft?/4* 7}a2a.2itte 



FIG. 15. 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, tympano- 



hyal; shy, stylohyal ; ehy, epihyal; chy, ceratohyal ; bhy, basihyal ; 



thhy, thyrohyal. The cartilage bones are shaded. {From Flower, 



after Huxley.) 



lachrymal, and palatine bones. It consists of four parts: 

 the paired ethmoturbinals or lateral ethmoids (Fig. 18), 

 the. mesethmoid, and the cribriform plate. The ethmotur- 

 binals are in the form of scroll-like laminae which project 

 forward from the transverse cribriform plate into the nasal 

 cavities. The portion which appears externally in the 

 medial wall of the orbit is the os planum. In the recent 

 state, the surfaces of these bones within the nasal cavity are 

 covered with a mucous membrane over which the first pair 

 of cranial nerves (olfactory) are distributed. The delicacy 



