THE SKULL AS A WHOLE 67 



The cranial region presents the temporal fossa, the zygomatic arch, and the 

 outer part of the i)etrous temporal bone. ^ 



The temporal fossa is bounded internally by the sagittal and frontal crests, 

 externally by the temporal crest and the zygomatic arch, and behind by the occipital 

 crest. Its upper and middle parts are rough for the attachment of the temporal 

 muscle. In its lower posterior part are several foramina which connnunicate with 

 the parieto-temporal canal. The fossa is continuous in front with the oi'bital cavity. 



The zygomatic arch is formed by the zygomatic processes of the temporal, 

 malar, antl maxilla. Its ventral face presents the condyle and glenoid cavity for 

 articulation with the lower jaw, through the medium of the articular disc. Behind 

 the glenoid cavity is th(^ post-glenoid process. 



The external auditory process projects outward through a deep notch in the 

 lower margin of the sciuamous temporal below the temporal crest. A little 

 further back is the mastoid process, crossed in its upper part by a groove for the 

 mastoid artery. 



The orbital region conii:)rises the orbit and the pter^'go-palatine fossa. 



The orbit is a cavity which incloses the eyeball, with the muscles, vessels, and 

 nerves associated with it. It is not separated in the skeleton from the temporal 

 fossa. The long axis of the cavity, taken from the optic foramen to the middle of 

 the inlet, is directed forward, outward, and slightly upward. The inner wall 

 (Paries medialis) is complete and extensive. It is concave and smooth, and is 

 formed by the frontal and lacrimal and the orbital wing of the sphenoid. In its 

 extreme anterior part is the fossa for the lacrimal sac. Behind this is a small de- 

 pression in which the inferior oblique muscle of the eye arises; here the plate which 

 separates the orbit from the maxillary sinus is very thin. The upper wall (Paries 

 superior) is formed l)y the frontal and to a small extent by the lacrimal bone. It 

 presents the supraorbital foramen, which perforates the root of the supraorbital 

 process. The lower wall (Paries inferior) is very incomplete, and is formed by the 

 malar, the zygomatic process of the temporal, and to a small extent by the maxilla. 

 The external boundary (Paries lateralis) is the supraorbital process. At the ex- 

 treme posterior part is the orbital group of foramina. Four are situated in front 

 of the pterygoid crest. Of these, the uppermost is the ethmoidal or internal 

 orbital foramen, which transmits the ethmoidal vessels and nerve. The optic 

 foramen is situated a little lower and further back; it transmits the optic nerve. 

 Immediately below the optic is the foramen lacerum orbitale, which transmits the 

 ophthalmic, third, sixth, and sometimes the fourth nerve; commonly there is a 

 very small trochlear or pathetic foramen in the crest for the last named nerve. 

 The foramen rotundum is below the foramen lacerum, from which it is separated 

 by a thin plate; it transmits the superior maxillary nerve. The alar canal opens 

 in common with the foramen rotundum, and the anterior opening of the pterygoid 

 or Vidian canal is also found here. The temporal foramen (For. alare parvum) is 

 just behind the pterygoid crest and on a level with the foramen lacerum. It is 

 the upper opening of a canal which leads from the alar canal, and through it the 

 anterior deep temporal artery emerges. The inlet of the orbital cavity (Aditus 

 orbitse) is circumscribed by a complete bony ring, which is nearly circular. Its 

 antero-inferior part (Margo infraorbitalis) is smooth and rounded; the remainder 

 (Margo supraorbitalis) is rough and irregularly notched. During life the cavity is 

 completed by the periorbita or ocular sheath, a conical fibrous membrane, the apex 

 of which is attached around the optic foramen. 



Below the orbital cavity is the pterygo-palatine fossa. Its wall is formed by 

 the pterygoid process, the perpendicular part of the palate bone, and the tuber 

 maxillare. Its deep anterior part (maxillary hiatus) contains three foramina. The 

 upper one, the maxillary foramen, is the entrance to the infraorbital canal, which 

 transmits the infraorl)ital nerve and vessels. The spheno-palatine foramen trans- 



