136 HEAD OF THE FOETUS. 



process, which is separate from the otlier parts and forms the 

 fourth piece. 



The sphenoidal bone may be separated by maceration into 

 three pieces. The body and the httle wings form one piece. 

 Each of the great wings, with the pterygoid processes united 

 to it, forms also a piece. The body of the bone is entirely 

 solid. 



A large part of the ethmoid is in a cartilaginous state. It is 

 divided into two portions by a partition of cartilage, which 

 occupies the place of the nasal plate and the crista galli. 



In consequence of the imperfect formation of the bones which 

 compose the vault of the cranium, there are several deficiencies 

 in it. Thus the superior anterior angles of the p'arietal bones 

 being incomplete, and also the upper angles of the pieces which 

 compose the os frontis, a vacuity with four sides is occasioned, 

 which is termed the 



Anterior fontanel. This opening may be distinguished by its 

 form, as well as its greater size, from another vacuity which is 

 produced in a similar way at the other end of the sagittal suture, 

 and called the 



Posterior fontanel: but as there are only three bones con- 

 cerned in its formation, viz. the two parietal and the occipital, 

 this vacuity is triangular. 



Besides these, there are. two other vacuities or fontanels on 

 each side, at the two lower corners of each parietal bone : these, 

 however, are much less than those first described. 



The smaller fontanels do not continue open long ; but the 

 anterior fontanel is seldom completely closed before the end of 

 the third year. 



It is very obvious upon an examination of the cranium, that 

 the centre of the base is better calculated to resist pressure than 

 any other part; as the cuneiform process of the occipital bone, 

 the petrous portion of the temporal, and the body of the sphe- 

 noidal bone, which compose a large part of it, are very firm and 

 substantial. 



T^he face of the foetus differs very essentially from that of the 

 adult. Although the orbits of the eyes are very large when 



