370 



MAMMALIAN ANATOMY 



The anterior surface faces upward and forward, and is convex from 

 side to side, more especially in the lower part. It is convex from 

 above downward in its narrower upper two-thirds, and flattened in its 

 widest part below. Small foramina for the transmission of vessels are 

 often present near the middle of the inner border, and on the outer 

 border at about the junction of the middle and lower thirds. 



The posterior surface of the nasal bone (Fig. 289) has the shape 

 of the external surface, but is shorter and, above, encroached upon by 



FIG. 289. 



Left Premaxillary. 



Left Premaxillo-m axillary Suture. 



Posterior Surface of Left Nasal Bone. 

 Ridge for Median Nasal Septum. 



Ridge for Partition of Mesial Scrolls, 



m. 



Upper Wall of Infra-orbital Foramen. 



Ridge on Maxillary for Ethmoidal 

 Cleft-plate. 



Nasal Process of Left Frontal Bone. 

 - - Fossa in Nasal and Frontal for An- 

 terior End of Ethmoidal Scroll, 1'. 



Fossa on Frontal for Scroll, I'. 



Ridge/or Upper Ethmoidal Parti- 

 tion, 1. 



Orbital Plate of Frontal. 

 Fossa for Ethmoidal Scroll, 1". 



Frontal Sinus. 



ROOF AND PART OF ANTERIOR WALL OF NASAL CHAMBER ; ETHMOID REMOVED. 



the superior border. Its inferior margin is also the inferior margin 

 of the external surface. The median border is straight, sharp, and 

 elevated, and forms, with the contiguous border of the other nasal, 

 the nasal crest, whereto is attached a part of the front of the inter- 

 nasal bony and cartilaginous septum. The external border, which is 

 nearly straight and directed obliquely downward and outward, is high 

 and somewhat rolled inward. It is usually broader below. It abuts 

 for the larger part of its length against the edge of the mesial par- 

 tition of the inner surface of the lateral ethmoid (Figs. 290, 291). 

 The posterior surface is deeply concave from side to side, forming a 

 curved roof for the anterior part of the nasal chamber and arching 

 over the front of the lateral ethmoid. 



The internal or median surface (Fig. 291) is perfectly flat and 



