64 OSSA PARIETALIA. 



These cavities are divided by a perpendicular bony partition, 

 which is sometimes perforated and admits a communication 

 between them. Their capacities are often very different in 

 different persons, and on the different sides of the same person. 

 In some persons whose foreheads were very flat, they are said 

 to have been wanting. They communicate with the nose by 

 means of a canal in the cellular part of the os ethmoides. 



The os frontis is composed *)f two tables, and an interme- 

 diate diploe, as the other bones of the cranium are : it is of a 

 mean thickness between the os occipitis and the parietal bones ; 

 and is nearly equally dense throughout, except the orbitar pro- 

 cesses, where, by the action of the eye on one side, and pressure 

 of the lobes of the brain on the other, it is made extremely thin 

 and diaphanous, and the diploe is entirely obliterated. In this 

 place there is so weak a defence for the brain, that fencers 

 esteem a push in the eye mortal. 



In such skulls as have the frontal bone divided by the sagittal 

 suture, the partition separating these cavities is evidently com- 

 posed of two plates, which easily separate. 



Each of the frontal sinuses opens into one of the uppermost 

 cells in the' anterior part of the ethmoid bone, and this cell 

 communicates with the middle channel of the nose under the 

 anterior end of the os turbinatum superius. 



This bone is united with the parietal, ethmoidal and sphe- 

 noidal bones of the head ; and with the nasal, maxillary, ungui- 

 form and malar bones of the face. 



Ossa Parietalia. 



Each of the two ossa parietalia is an irregular square ; its 

 upper and front edges being longer than the one behind or 

 below. The inferior edge is concave, the middle part receiving 

 the upper round part of the temporal bone. The angle formed 

 by the under and anterior edges is so extended as to have the 

 appearance of a process. 



The external surface of each os parietale is convex. Upon 

 it, somewhat below the middle height of the bone, there is a 



