86 BASE OF THE SKULL. 



frontal bone and by the malar bone, and below by the zygoma. It is 

 formed by part of the frontal, great wing of the sphenoid, parietal, squa- 

 mous portion of the temporal, malar bone, and zygoma, and lodges the 

 temporal muscle with the deep temporal arteries and nerves. 



The mastoid portion is rough, for the attachment of muscles. Upon its 

 posterior part is the mastoid foramen, and below, the mastoid process. 

 In front of the mastoid process is the external auditory foramen, surrounded 

 by the external auditory process ; and 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 exter- 

 nal 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 con- 

 tains the external pterygoid, with part of the temporal and internal ptery- 

 goid muscle, and the internal maxillary artery and inferior maxillary nerve, 

 with their branches. On the inner and upper side 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. It is completed externally by the malar 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 the tuberosity of the superior maxillary bone, and transmits the inter- 

 nal maxillary artery. At the angle of junction of these two fissures is a 

 small space, the spheno-maxillary fossa, bounded by the sphenoid, palate, 

 and superior maxillary bone. In this space are seen the openings of five 

 foramina, the foramen rotundum, spheno-palatine, pterygo-palatine, pos- 

 terior palatine, and Vidian. The spheno-maxillary fossa lodges MeckePs 

 ganglion and the termination of the internal maxillary artery. 



The BASE OF THE SKULL presents an internal or cerebral, and an exter- 

 nal 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 corresponds 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 of the sphenoid. The 

 latter and the lesser wings 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 ; immediately 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 opthalrnic nerve. Farther back in the middle line is the processus 

 olivaris, and on the sides of this process the optic foramina, anterior and 

 middle clinoid processes, 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 bv the petrous and squamous portion 



