THE BONES OF THE HEAD 137 



and vessels. (4) The opening of the infra-orbital canal, on the 

 floor, transmitting the infra-orbital nerve and vessels. (5) The 

 opening of the temporal canal, and (6) the opening of the 

 malar canal, both on the outer wall, for the branches of the 

 temporo-malar or orbital nerve from the superior maxillary division 

 of the fifth cranial nerve. (The temporal and malar openings 

 may be combined into one.) (7) The spheno-maxillary fissure, 

 at the junction of the outer wall and floor, which transmits the 

 superior maxillary nerve to become the infra- orbital, and the infra- 

 orbital vessels. (8) The lachrymal canal, at the anterior part of the 

 inner wall, for the nasal duct. (9) The anterior ethmoidal canal, 

 and (10) the posterior ethmoidal canal, both situated on the inner 

 wall, the former transmitting the nasal nerve and anterior ethmoidal 

 vessels, and the latter the posterior ethmoidal vessels and the 

 spheno-ethmoidal nerve. 



Eight muscles take their origin within each orbit. The four recti 

 arise from a fibrous ring surrounding the optic foramen. The 

 levator palpebrae superioris arises above and in front of the optic 

 foramen, and the superior oblique arises internal to the last named. 

 The inferior oblique arises from the depression at the anterior and 

 inner part of the floor, external to the orifice of the lachrymal 

 canal, and the tensor tarsi arises from the lachrymal crest behind the 

 lachrymal groove. 



The Nasal Fossae. — The nasal fossae are two in number, right and 

 left, and they lie on either side of the median plane. They extend 

 horizontally from before backwards, opening on the face as the 

 anterior nares by means of the anterior nasal aperture, and com- 

 .municating posteriorly with the naso-pharynx by the posterior 

 nares. The vertical and antero-posterior dimensions of each fossa 

 greatly exceed the transverse. The two fossae are separated from 

 each other by a partition, called the septum nasi, which is partly 

 osseous and (in the recent state) partly cartilaginous. Each fossa 

 presents a roof, floor, and two walls, inner and outer. 



The roof over its central part is horizontal but in front and behind 

 it is inclined downwards. Six bones enter into its formation. The 

 central portion is formed by one-half of the cribriform plate of the 

 ethmoid. The sloping anterior part is formed by the grooved ala of 

 the frontal bone by the side of the nasal spine, and the posterior 

 surface of the nasal bone. The sloping posterior part is formed by 

 portions of the anterior and inferior surfaces of the body of the 

 sphenoid, the ala of the vomer, and a part of the sphenoidal pro- 

 cess of the palate bone. The central part of the roof is perforated 

 by the foramina of one-half of the cribriform plate, including the 

 nasal slit, and, at its back part, the aperture of the sphenoidal air 

 sinus opens into the spheno-ethmoidal recess. 



The floor is smooth and concave from side to side. Over its 

 anterior three-fourths it is formed by the palatal process of the 

 superior maxilla, and over its posterior fourth by the horizontal 

 plate of the palate bone. Near its anterior extremity, close to 



