44 BOXES OF THE HEAD. 



The anterior border, thin and serrated, articulates uith the orbital 

 plate of the frontal bone. The posterior border is prominent and free,, 

 and forms the boundary bet^Yeen the anterior and middle cranial fossa?, 

 terminatino- internally in a smooth rounded knob, the anterior clinoid 

 process. Below and to the inside of this is the optic foramen. 



The pterygoid processes project downwards and slightly forwards, 

 between the body and the great wings. Each consists of two plates 

 united in front and diverging behind, so as to enclose between them 

 the ]ifer!/f/oid fo.^sa. The external j^forijf/okl plaie, broader than the 

 internal, lies in a plane extending backwards and outwards ; its outer 

 surface bounds the zygomatic fossa, and gives attachment to the 

 external pterygoid muscle. The internal pterygoid muscle arises from 

 its inner suri^ice. The infernal pfcrijf/oid plate is longer and narrower 

 than the external, and is prolonged into the slender hook-like or 

 hrfmiikirjrrocrss, round which in a groove plays the tendon cf the tensor 

 palati muscle. At its base, the internal plate turns inwards beneath 

 the bodv, from which its extremity remains distinct as a slightly raised 

 ed^-e, w'hich articulates with the everted margin of the vomer ; and 

 externally to this it is marked by a small groove, which contributes 

 with the ]\alate bone to form the pieri/fjo-palafine canal The interval 

 between the lower ends of the pterygoid plates is occupied by the 

 pyramidal process of the palate bone. At the base of the internal 

 pterygoid process is a slight depression, distinguished as the navicular 

 foss(f,'^\vh\ch gives attachment to the tensor ])alati muscle. 



Fissures and foramina. — Each lateral half of the bone presents a 

 fissure, four foramina, and a canal. The sphenoidal fissure is the 

 obliquely placed elongated interval between the great and the small 

 wing ; it is closed externally by the frontal bone, so as to form the 

 foremen laceriim orbifale ; it opens into the orbit, and transmits the 

 "third, fourth, and sixth nerves, the ophtlialmic division of the fifth 

 nerve, and the o]ihthalmic vein. Above and to the inside of it is the 

 optic foramen, Avhich is inclined outwards and forwards from the side of 

 the olivary process, pierces the base of the small wing, and transmits the 

 optic nerve and the ophthalmic artery. The foramen rotundum is. 

 directed forwards through the great wing, below the sphenoidal fissure ; 

 it opens immediately below the level of the orbit, and transmits the 

 superior maxillary division of the fifth nerve. The foramen ovale is 

 large, placed behind and a little external to the foramen rotundum, 

 near the posterior margin of the great wing ; it is directed downwards, 

 and transmits the inferior maxibary division of the fifth nerve. The 

 foramen .phwswn is a small foramen piercing the great wing, near its- 

 posterior angle, and transmits the middle meningeal vessels. 



The Vid/an or pferi/r/oid canal, passes through the bone horizontally 

 from before backwards at the base of the internal pterygoid plate; it 

 opens a,nteriorly into the spheno-maxillary fossa, and posteriorly into 

 the foramen lacerum medium, and transmits the Vidian nerve and 

 vessels. 



"Varieties.— Spicula of bone sometimes connect the anterior clinoid process 

 -n-itli the pituitary fossa and with the posterior clinoid process. The outer ptery- 

 goid plate is sometimes connected by a bi-idge of bone or of ligament ydt\\ the- 

 spinous process. The foramen ovale and foramen spinosum are frequently in- 

 complete at the posterior margin of the bone. 



