X.] MAN. 133 



are short, and nearly vertical, broad below and narrow 

 above. The anterior nares are also nearly vertical. The 

 turbinal bones are comparatively little developed, and of 

 simple structure, especially the lower or maxillo-turbinal 

 {MT). The flat bony-plate on the outer side of the ethmo- 

 turl)inal or -'os planum," instead of lying against the inner 

 side of the maxilla, forms part of the outer wall of the nasal 

 cavity and inner wall of the orbit, uniting with the frontal 

 above, the lachrymal in front, the maxilla below, and the 

 palatine behind. 



The group of bones placed around the organ of hearing, 

 i)eriotic, squamosal, and tympanic, though originally dis- 

 tinct, become united together soon after birth, to form the 

 so-called " temporal bone." They differ from the corre- 

 sponding bones in the Dog in the following particulars. The 

 periotic has a very much larger mastoid portion (/!/), which 

 forms a considerable part of the wall of the cerebellar fossa. 

 In the new-born infant its outer surface is smooth 

 and flat, but as life advances, air-cells become developed 

 within it, communicating with the tympanic cavity, and 

 a strongly-marked descending projection, the " mastoid pro- 

 cess," appears on the lower and anterior part of its outer 

 surface. The squamosal {Sq) is a large flat vertical plate, 

 forming a considerable part of the wall of the posterior 

 cerebral fossa, behind the alisphenoid. Its zygomatic pro- 

 cess is comparatively slender and straight. The tympanic 

 forms a long tubular external auditory meatus, but its inner 

 part joins the periotic, forming the floor of the tympanic 

 cavity without being inflated into an auditory bulla. Its 



tlie Ijones the suture is always evident at birth, and can often be traced 

 even in adult skulls. See G. W. Callender " On the Formation and 

 Early Growth of the Bones of the Human Face." (Phil. Trans. 1869, 

 p. 163.) 



