130 SKELETON. 



4. Temporal Bones, (Ossa Temporum, Temporaux.) 



These bones form portions of the inferior lateral parietes, and 

 of the base of the cranium. 



Their figure is very irregular. Their circular anterior por- 

 tion is called squamous : behind it is the mastoid, and between 

 the others is the petrous. 



The squamous portion is thinner than the other bones of the 

 cranium that have been described, from the temporal muscle and 

 its fascia covering it, so as to afford sufficient protection to the 

 brain. Its exterior surface is smooth and slightly convex. The 

 interior surface is formed into fossa? by the convolutions of the 

 brain. At the anterior inferior part of the latter surface, a 

 groove is made by the middle artery of the dura mater, imme- 

 diately after it gets from the foramen spinale of the sphenoid 

 bone on its way to the parietal. This groove bifurcates, one 

 branch runs backwards to join the posterior groove of the pa- 

 rietal bone; and the other ascends to join the anterior groove 

 of the same, frequently, however, impressing the top of the 

 great wing of the sphenoid, just before it reaches the parietal. 

 The greater part of the circumference of this portion is sloped 

 to a sharp edge, but at the anterior inferior part it is serrated 

 and thicker. On the outside of the latter is the glenoid cavity, 

 for articulating with the lower jaw: the length of it is trans- 

 verse, with a slight inclination backwards, so that a line drawn 

 through it would strike the foramen magnum occipitis. The 

 anterior margin of this cavity is formed by a tubercle, on which 

 the condyle of the lower jaw rises when the mouth is widely 

 opened. The outer margin of the glenoid cavity is formed by 

 the root of the zygomatic process. The zygomatic process has 

 a broad horizontal root, from which it extends outwardly, and 

 then diminishing, runs forwards to join the malar bone. Pos- 

 terior to the root of the zygomatic process, a small vertical 

 groove may be seen occasionally, made by the middle tempo- 

 ral artery. 



The mastoid portion of the temporal bone, is thick and cel- 

 lular. Its upper part forms an angle, which is received between 

 the parietal and occipital bones: both margins of this angle are 



