490 



MAMMALIAN ANATOMY 



pierced by a foramen for the tip of the upper outer scroll of the lateral 

 ethmoid. Below the cribriform plate is the opening leading backward 

 into the sinus in the body of the presphenoid, which is filled by the 

 lowest scroll of the ethmoid. The cribriform plate exhibits the small 

 olfactory openings. 



The floor of each nasal fossa is oblong, and is more than twice as 

 long as wide (Fig. 397). It is formed by the premaxillary bone and 

 the palatine processes of the maxillary and palatine bones. Its median 

 line is straight, and for the anterior two-thirds is elevated into a crest 

 to give attachment to the vomer and the septal cartilage. At its outer 

 arcuate edge the floor turns up abruptly behind into the outer wall. 

 The emarginate posterior edge is the lower edge of the posterior nares. 

 The floor is almost flat, and slopes slightly downward at the posterior 

 part. In front, near the inner border, is the large oval anterior 

 palatine foramen ; beyond this is the elevated transverse ridge which 

 forms the lower lip of the anterior naris. The floors of the two nasal 

 fossae are confluent at the posterior third, behind the attachment of 



the vomer. 



FIG. 396. 



Left Premaxillary. 



Left Premaxillo-m axillary Suture. 



Posterior Surface of Left Nasal Bone. 

 /Wv --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. 



Kasal Process of Left Frontal Bone. 

 Fossa in JVoi and Frontal for An- 

 terior End of Ethmoidal Scroll, 1'. 



Fossa on Frontal for Scroll , 1'. 



Ridge for 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 roof (Fig. 396) of each nasal fossa consists of two parts, a 

 shorter, narrow anterior part, consisting of the concave posterior sur- 

 face of the nasal bone, and a longer and wider posterior part, which 

 is the under surface of the horizontal portion of the frontal lying 



