x.] MAN. 155 



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- 

 turbinal 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 lacrymal in front, the maxilla below, and the 

 palatine behind. 



The group of bones placed around the organ of hearing, 

 periotic, 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 (J/), 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 process," 

 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 process is com- 

 paratively slender and straight The tympanic forms a 

 long tubular external auditory meatus, but its inner part 



before birth, so that no trace of the maxillo-premaxillary suture is ever 

 seen on the outer side of the face. On the inner and palatal aspect of 

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

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

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

 p. 163.) Also : P. Albrecht, " Sur la fente maxillaire et les os inter- 

 maxillaires," etc. 1883. 



