THE CAVITY OF THE CRANIUM. 125 



cuous. It extends almost from one opening of the nose to the 

 other. Under this bone is the third and largest channel or infe- 

 rior meatus of the nose. It is made large by an excavation of 

 the upper maxillary bone, particularly at the anterior part. It 

 affords a direct and very easy passage to the posterior opening of 

 the nose and the throat. 



Near the anterior extremity of this meatus is the lower orifice 

 of the lachrymal duct, which is so situated that a probe properly 

 curved can be readily passed into it through the nostril. 



There are, then, four foramina on each side, which form com- 

 munications between the cavities of the nose and the adjacent 

 cells, viz. 



One in the upper meatus, which leads to the posterior ethmoid 

 cells. 



A second in the middle meatus, which leads to the anterior 

 ethmoid cells and the frontal sinuses. 



A third in the same meatus, which opens into the maxillary 

 sinus. 



A fourth in the anterior surface of the body of the sphenoidal 

 bone, which opens into the sphenoidal sinus. 



To these must be added the opening of the lachrymal canal. 



It will be moat useful to the student of anatomy, after placing three or four of 

 the uppermost cervical vertebrae in their natural situation, to take a view of 



The Cavity between the spine and the posterior Nares, which 

 is bounded above, by the cuneiform process, passing obliquely 

 upward and forward ; laterally, by soft parts not yet described ; 

 behind, by the bodies of the cervical vertebrae ; and before, by 

 the posterior nares, each of which is oblong in form, rounded 

 above, flat below, and separated from the other by a thin parti- 

 tion, the vomer. 



The Cavity of the Cranium. 



The upper concave surface of this cavity corresponds with 

 the figure of the cranium. The ridge in it for supporting the fal- 

 ciform process of the dura mater, the groove made by the longi- 

 tudinal sinus, the impressions of the arteries, and the pits made 

 by the convolutions of the brain, are particularly to be noticed. 

 11* 



