42 



BO:N T ES OF THE HEAD. 



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 a large 

 foramen, external and posterior to the foramen rotundum, situated near 

 the posterior margin of the great wing, and directed downwards ; it transmits 

 the inferior maxillary division of the fifth nerve. The foramen spinosum 

 is a small foramen immediately external and posterior to the foramen ovale ; 

 it pierces the posterior angle of the great wing, and transmits the middle 

 meningeal vessels. 



The Vidian, or pteryyoid canal, passes through the bone horizontally 

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

 anteriorly into the spheno-maxillary fossa, and posteriorly into the foramen 

 lacerum medium, and transmits the Vidian nerve and vessels. 



Varieties. The groove of the internal carotid artery on the inner aspect of the 

 anterior clinoid process is frequently converted into a foramen by a spiculum of bone 

 stretching outwards to that process from the side of the pituitary fossa, and forming 

 what has been called the middle clinoid process ; and in cases where this occurs 

 another spiculum is sometimes found, uniting the anterior and posterior clinoid pro- 

 cesses. In many cases a third spiculum, the lingula (Henle), projects backwards from 

 the posterior extremity of the carotid groove outside the artery. A bridge of bone, 

 or of ligament, sometimes passes from the margin, and sometimes from the extremity 

 of the external pterygoid plate to the spinous process. The foramen ovale and foramen 

 spinosum are frequently open behind. 



ETHMOID BONE. 



The ethmoid, or sieve-like bone, projects down wards from between the orbital 

 plates of the frontal bone, and enters into the formation of the cranium, the 



orbits, and the nasal fossae. It is of a cu- 

 boid figure. It is exceedingly light for its 

 size being composed of very thin plates 

 of bone and a collection of irregular 

 cells. It consists of a central vertical 

 plate, and of two lateral masses, united 

 at their superior extremities by a horizon- 

 tal cribriform lamella. 



Fig. 37. THE ETHMOID BONE, f 



A, from the right side. 1, crista galli ; 2, 

 vertical plate ; 3, cribriform plate and foramina ; 

 4, orbital plate or os planum ; 5 5, the uncinate 

 process ; 6, the superior, and 7, the inferior 

 turbinated bone ; 8, the anterior, and 9, the 

 posterior ethmoidal groove or foramen. 



B, the ethmoid bone from behiud. The in- 

 dications where marked are the same as in A. 

 10, the lateral or cellular part of the bone ; 11, 

 its posterior surface of union with the sphenoidal 

 turbinated and palate bones. 



It articulates with thirteen bones : the 

 frontal, sphenoid and vomer, the nasal, 

 lachrymal, superior maxillary, palatal, and inferior turbinated bones. 



The CENTRAL PLATE lies in the mesial plane, and forms the upper part of 

 the septum of the nose. Its superior margin appears in the cranial cavity, 

 above the cribriform lamella, in the form of a ridge which rises anteriorly 

 into a thick process, the crista galli, to which the falx cerebri is attached. 



i- 37. 



