220 HUMAN ANATOMY. 



roof of the pharynx. On either side of it is a rent separating it from the temporal 

 bone. The back of this rent is l\\e Jugular forame7i ; then comes ih^Jissure proper ; 

 and, at the apex of the petrous portion, the middle lacerated foram&ti, which in hfe is 

 filled with cartilage, as is also the fissure. Outside, in the petrous bone, is the 

 carotid openings internal to the tympanic plate, which is separated by the fissure of 

 Glaser from the gleyioid fossa. The outer border of the petrous forms a gutter 

 with the great wing of the sphenoid for the cartilaginous^ part of the Eustachian 

 tube. Just outside of this is the foramen spinosimi, often in the suture between 

 the sphenoid and temporal, and before it the fora77ien ovale. In the front part of the 

 base outside of the pterygoid is that part of the great wing which looks downward, 

 overhanging the zygomatic fossa. 



THE INTERIOR OF THE CRANIUM. 



The vault^ of the cranium has the groove for the superior longitiidinal sinus 

 in the middle, with Pacchionian depressio7is on each side of it. The grooves for the 

 middle meningeal artery cover the parietal region. The base of the cranium is 

 divided into three fossae, — the anterior, the middle, and thepostefior. 



The anterior fossa ^ is bounded behind by the line in front of the olivary emi- 

 nence and by the edge of the lesser wings of the sphenoid. It has a deep hollow 

 over the nasal cavity, the floor of the depression being the cribriform plate of the 

 ethmoid. In the median line are the crista galli and the foramen caecum. The 

 lateral part of the anterior fossa slants downward, inward, and backward, and is quite 

 smooth* in the middle behind the hollow. 



The middle fossa ^ is limited in the centre to the sella turcica, but expands at 

 the sides. It is separated from the posterior fossa by the dorstim sellce and the 

 superior border of the petrous. The middle fossa has the olivary eminence and the 

 optic foramiyia in front of the sella turcica, at each side, of which is the ^r^^z'^ for the 

 internal carotid artery and the cavernous sinus. The clinoid processes tend to meet 

 above its sides, and sometimes do so, especially when the middle clinoid is developed. 

 On the anterior border of the fossa, near the middle, is the sphenoidal fissure opening 

 into the orbit. Just behind its inner end is the foramen rotundum ; farther back and 

 outward are the foramen ovale and foramen spinosum, from which latter start the 

 grooves of the middle meningeal artery ; more internal lies the middle lacerated 

 foramen. The depression for the Gasserian ganglion is seen at the apex of the 

 anterior surface of the petrous portion of the temporal bone ; the ganglion is very 

 conveniently placed for its ophthalmic, superior maxillary, and mandibular branches 

 to reach the sphenoidal fissure, the foramen rotundum, and the foramen ovale re- 

 spectively. 



The posterior fossa ^ is much the larger. In the middle is the for ante n mag- 

 num, with the basilar groove before it. The impression for the superior peti^osal 

 sinus is at the top of the petrous. The inferior petrosal sintis lies on the suture 

 between the petrous bone and basilar process. The internal atiditory ineatus, the 

 jugular forameyi, and the ayiterior condyloid foramen are very nearly in a vertical 

 line. The impressions for the lateral sinuses run outward from the internal occipital 

 protuberance until they suddenly turn downward, making a deep groove in the tem- 

 poral bone. The course of .the second portion of the sinus is straight downward 

 and inward, the highest point of the sinus corresponding with the supramastoid crest 

 above the middle of the mastoid process. This point is sometimes so near to the 

 surface that the bone is translucent. In its descent the sinus may for a time keep 

 near the surface, or leave it at once. There is much variation in many respects ; 

 sometimes the downward turn of the sinus is less sharp. The claim that anything 

 can be predicated of this from the shape of the head is extremely uncertain. Just 

 before reaching the jugular foramen the sinus once more changes its direction, 

 running forward and upward. 



THE ARCHITECTURE OF THE CRANIUM. 

 The curved vault of the skull is well adapted to break shocks, but the base 

 is much weaker ; not only is the bone thin in many places, but it is interrupted by 



^ Calvaria. ^ Fossa cranii anterior. ^ F. craaii media. 4 F. craaii posterior. 



