SURFACE OF THE HEAD. 161 



parated by the inferior ridge of the occipital cross. The lambdoi- 

 dal suture traverses these fossae. At the junction between the 

 petrous bone and the basilar process of the occipital, in the course 

 of the suture, is a groove for the inferior petrous sinus. The 

 groove conducts to the posterior foramen lacerum, which has a 

 small part separated from it by the little spine of the petrous bone, 

 which, with the assistance of the dura mater," forms a distinct 

 foramen for the eighth pair of nerves. The posterior foramen 

 lacerum beingcommon to the temporal and occipital bones, is oc- 

 casionally much larger on the right than on the left side: in 

 which case, the groove that leads from it along the angle of the 

 temporal bone, the inferior corner of the parietal, and the hori- 

 zontal limb of the occipital cross, is also larger. Above the fo- 

 ramen lacerum are the meatus auditorius internus and the inter- 

 nal orifice of the aqueduct of the vestibule. Between the foramen 

 lacerum and foramen magnmn occipitis is the anterior condyloid 

 foramen. The two posterior fossae of the base of the cranium 

 contain the cerebellum. 



SKCT. IV. OF THE EXTERNAL SURFACE OF THE HEADi 



Anatomists, of modern times, consider the external surface 

 of the head as forming or representing three ovals and two 

 triangles each of which constitutes a region. The first oval is 

 the whole superior convex part of the cranium ; or, in other 

 words, the external surface of its vault. The second oval is 

 formed by the inferior surface of the cranium, and of the face. 

 The third oval -is formed by the lower front part of the os fron- 

 tis, and by the face. Each side of the head forms one of the 

 triangular regions. 



The superior region is so simple, and its parts have been so 

 closely sketched, that it is unnecessary to repeat the descrip- 

 tion. 



The inferior region or oval, extends from the chin to the oc- 

 cipital protuberance, and is bounded in its transverse diameter 

 by the superior semicircular ridges of the os occipitis, by the 

 mastoid processes, and by the rami and base of the lower jaw. 

 This surface is subdivided into Palatine, Guttural, and Occipital 

 sections or regions. 



The Palatine region or section, is formed by the superior 



14* 



