BASE OF THE SKULL. 57 



in front of this foramen the glenoid cavity, bounded above by the 

 middle root of the zygoma, and in front by its tubercle. 



The zygomatic portion, or fossa, is the irregular cavity below the 

 zygoma, bounded in front by the superior maxillary bone, internally 

 by the external pterygoid plate, above by part of the great wing of 

 the sphenoid and squamous portion of the temporal bone, and by the 

 temporal fossa, and externally by the zygomatic arch and ramus of 

 the lower jaw. It contains the external pterygoid, with part of the 

 temporal and internal pterygoid muscle, and the internal maxillary 

 artery and inferior maxillary nerve, with their branches. At the 

 bottom of the zygomatic fossa are two fissures, the spheno-maxillary 

 and the pterygo-maxillary. 



The spheno-maxillary fissure is horizontal in direction, opens into 

 the orbit and is situated between the great ala of the sphenoid and 

 the superior maxillary bone. 



The pterygo-maxillary fissure is vertical, and descends at right 

 angles from the extremity of the preceding. It is situated between 

 the pterygoid process and tuberosity of the superior maxillary bone, 

 and transmits the internal maxillary artery. At the angle of junc- 

 tion of these two fissures is a small cavity, the spheno-maxillary 

 fossa, bounded by the sphenoid, palate, and superior maxillary bones, 

 in which are seen the openings of five foramina, the foramen ro- 

 tundum, spheno-palatine, pterygo-palatine, posterior palatine, and 

 Vidian. It lodges Meckel's ganglion and the termination of the in- 

 ternal maxillary artery. 



The base of the skull presents an internal or cerebral, and an ex- 

 ternal or basilar surface. 



The cerebral surface is divisible into three parts, which are named 

 the anterior, middle, and posterior fossa of the base of the cranium. 

 The anterior fossa is somewhat convex on each side, where it cor- 

 responds with the roofs of the orbits ; and concave in the middle, 

 in the situation of the ethmoid bone, and the anterior part of the 

 body and lesser wings of the sphenoid, which constitute its posterior 

 boundary. It supports the anterior lobes of the cerebrum. In the 

 middle line of this fossa, at its anterior part, is the crista galli, im- 

 mediately in front of this process, the foramen ccecum, and on each 

 side the cribriform plate, with its foramina, for the transmission of 

 the filaments of the olfactory and nasal branch of the ophthalmic 

 nerve. Farther back in the middle line is the processus olivaris, and 

 on the sides of this process the optic foramina, anterior clinoid pro- 

 cesses, and vertical grooves for the internal carotid arteries. 



The middle fossa of the base, deeper than the preceding, is 

 bounded in front by the lesser wing of the sphenoid ; behind, by the 

 petrous portion of the temporal bone ; and is divided into two lateral 

 parts by the sella Turcica. It is formed by the posterior part of 

 the body, great ala, and spinous process of the sphenoid, and by the 

 petrous and squamous portion of the temporal bones. In the centre 

 of this fossa is the sella Turcica, which lodges the pituitary gland, 

 bounded in front and behind by the anterior and posterior clinoid 



8 



