THE SKULL THE CRANIUM 



289 



FIG. 209. 



on each side of which are fastened the nasal bones. The nasal process 

 of the maxillary has a small sutural attachment to the front of the 

 internal angular process. 



The orbital surface of the vertical plate is more deeply concave in 

 its outer part for the reception of the lachrymal gland. Near its 

 medial anterior corner are a tubercle and a pit for the attachment 

 of the trochlearis or superior oblique 

 muscle of the eyeball. Between the 

 internal angular process and the nasal 

 spine is the opening to the frontal sinus. 

 Behind this opening the medial margin 

 of the orbital plate is wide and impressed 

 by the upper surface of the lateral eth- 

 moid. It is crossed by two grooves 

 which the ethmoid converts into the 

 anterior and posterior ethmoidal fora- 

 mina. The space between the medial 

 margins of the two bones is known as 

 the ethmoidal notch. 



The external angular process unites 



,-i ,T i ,1 r> , i nioiuai iioicn ; a, superior uemaiea ooraer, 



With the malar, thus forming the Upper articulating with the parietal bones; 4, pos- 



part of the lateral orbital wall. 



INTERNAL VIEW OF THE FRONTAL 

 BONE. 



1, groove for the longitudinal sinus, narrow- 

 ing below on the frontal crest, 2, in the eth- 

 moidal notch ; 3, superior dentated border, 



terior border of the orbital plate, 5, which 

 joins the small wing of the sphenoid bone; 

 6, irregular inner border of the same plate, 

 which covers the upper part of the eth- 

 moidal scrolls ; 7 points to the position of 

 the ethmoidal foramina; 8, nasal spine; 9, 

 thick rough border articulating with the great 

 wing of the sphenoid bone ; 10 refers to the 

 black spot, which indicates the position of a 

 fossa for the pulley of the trochlearis muscle ; 

 to its outer side is the supraorbital notch ; 

 11, internal angular process, and entrance 

 to the frontal sinus; 12, external angular 



THE ETHMOID. 



General Description. The Eth- 

 moid is a cubical, bilaterally symmetrical 

 bone which almost completely fills the 

 nasal cavity (Fig. 210). It is without pr0 cess. 

 distinct processes, and consists almost 



entirely of a mass of thin, delicate scrolls of bone, whereby the super- 

 ficial area of the wall of the nasal cavity is largely increased, inas- 

 much as the mucous membrane which covers the wall invests every 

 separate scroll. In other words, every scroll is lined by the mucous 

 membrane of the nasal cavity, and thereby contributes to this great 

 increase of the superficial area of the nasal wall. Its posterior surface, 

 which can be recognized as the curved sieve-like plate, forms part of 

 the anterior wall of the cranial cavity, filling the gap left between the 



frontals above and at the side and the presphenoid below (Fig. 200). 



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