EXTERIOR OF THE SKULL. 57 



directed forwards and outwards, their inner walls being nearly parallel, and 

 their outer walls diverging so much as to be at right angles one to the other. 

 The roof of each orbit is formed by the orbital process of the frontal and the 

 small wing of the sphenoid bone ; the floor consists of the orbital processes 

 of the malar and superior maxillary bones, and of the small orbital surface 

 of the palate bone at the back part ; the inner wall consists of the ascending 

 process of the superior maxillary, the lachrymal, the ethmoid, and the 

 sphenoid bone ; and the outer wall of the orbital surfaces of the malar bone 

 and great wing of the sphenoid. The sphenoidal fissure (foramen lacerum 

 orbitale), at its inner extremity, occupies the apex of the orbit, while its 

 outer and narrower part lies between the roof and the external wall. The 

 foramen opticum is internal and superior to the sphenoidal fissure. In the 

 angle between the external wall and the floor is the spheno-maxillary fissure, 

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

 leading into the spheno-maxillary fossa at its back part, and the zygomatic 

 fossa at its fore part. Passing forwards from the margin of the spheno- 

 maxillary fissure is the commencement of the infra-orbital canal, grooving 

 the posterior part of the floor of the orbit. At the fore part of the inner 

 wall is the lachrymal groove, formed by the superior maxillary and lachrymal 

 bones, and leading into the nasal duct : further back, between the ethmoid 

 and frontal bones are the anterior and posterior internal orbital foramina ; 

 in the anterior margin of the roof is the supra-orbital foramen or notch ; 

 and in the outer wall are the minute foramina which perforate the malar bone. 



The LATERAL REGION" of the skull presents in a horizontal line from 

 behind forwards the mastoid process, the external auditory meatus, the 

 glenoid fossa, with the condyle of the lower jaw, and the zygomatic or 

 malar arch, formed by the zygomatic process of the temporal bone and the 

 posterior part of the malar. When the head of the lower jaw is in the 

 glenoid cavity, the coronoid process lies internal to the malar arch. The 

 upper part of the space bridged over by this arch is called the temporal 

 fossa, the lower part the zygomatic fossa, the line of division being the rough 

 ridge which divides the external surface of the great wing of the sphenoid 

 bone into an upper and lower portion. The temporal fossa is occupied by 

 the temporal muscle ; it is bounded superiorly by the temporal ridge ; and 

 the frontal, parietal, sphenoid and malar bones take part in its formation. 

 The zygomatic fossa is occupied in part by the external pterygoid muscle ; 

 its wall is formed internally by the external pterygoid plate, superiorly by 

 the lower part of the great wing of the sphenoid bone, and anteriorly by the 

 superior maxillary. Inferiorly the external pterygoid plate comes nearly 

 into contact with the superior maxillary bone, but is usually separated from 

 it, though not always, by a thin portion of the pyramidal process of the 

 palate bone; superiorly, it is divided from it by the ptery go-maxillary 

 fissure, a vertical opening, which leads into the spheno-maxillary fossa, and 

 which is continued above into the outer extremity of the horizontal spheno- 

 maxillary fissure opening into the orbit. 



The spheno-maxillary fossa is the space which lies in the angle between 

 the pterygo-maxillary fissure and the inner or posterior half of the spheno- 

 maxillary fissure. It is bounded posteriorly by the external pterygoid 

 process and inferior division of the anterior surface of the great wing of 

 the sphenoid bone, anteriorly by the tuberosity of the superior maxillary 

 bone, and internally by the vertical plate of the palate bone. Into this 

 narrow space five foramina open, viz., on the posterior wall, the foramen 

 rotund urn, the Vidian canal, and, between the sphenoidal process of the 



