THE SKULL AS A WHOLE 69 



part of the body of the sphenoid; it supports the frontal lobes 

 of the cerebrum. It is convex laterally, with a slight con- 

 cavity over the cribriform plate excepting where the crista 

 galli stands up separating the olfactory grooves. Here are 

 found the foramen cecum, the olfactory foramina, openings of 

 the internal orbital or ethmoidal canals, and the foramen for the 

 nasal nerve. 



The middle fossa is on a lower level than the anterior, and 

 consists of a median and two lateral parts. The median part 

 is narrow, presenting the olivary eminence, the sella Turcica, 

 and limited behind by the dorsum sellse. Laterally is the 

 great wing of the sphenoid, the squama, and anterointernal 

 surface of the petrous portion. This lodges the temporal 

 lobe of the cerebrum. The foramina present are the optic, 

 sphenoidal fissure, foramen rotundum, ovale, spinosum, lacerum, 

 and hiatus Fallopii. 



The posterior fossa is deeper and larger than the others, 

 and lodges the cerebellum, medulla, and pons. The occipital 

 bone, the petrous and mastoid portions of the temporal, postero- 

 inferior angle of the parietal, and body of the sphenoid enter 

 into it. In the centre is the foramen magnum, and on each 

 side, in a nearly vertical line, are the anterior condylar fora- 

 men, jugular foramen, and internal auditory meatus. Behind 

 the jugular foramen is the posterior condylar (if present), 

 and higher up the mastoid foramen, both opening into the 

 lateral sulcus. By the internal auditory meatus the facial 

 and auditory nerves, the portio intermedia, and the auditory 

 vessels leave the cranium. 



Besides these points mentioned there are grooves for arteries 

 and venous sinuses. 



That for the middle meningeal artery commences at the 

 foramen spinosum, and passes anteriorly to the great wing 

 of the sphenoid, and posteriorly upon the squama and parietal. 

 There is also the groove for the internal carotid artery on the 

 side of the body of the sphenoid, the groove for the superior 

 longitudinal sinus terminating at the internal occipital pro- 

 tuberance, those for the lateral sinuses, and others for the 

 superior and inferior petrosal sinuses on the petrous portion. 



The nasal cavities, or the nasal fossae, are placed one on 

 each side of a median vertical septum. They open in front 

 by the anterior nasal aperture and behind by the posterior 



