76 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 98. — A frontal section through the anterior part of the skull, showing the orbits, the nasal fossae, 



and the maxillary sinuses (f). 

 Fig. 99. — The floor of the left orbit seen from above, the roof having been removed (|). 

 Fig. 100. — The maxilla, palate bone, and lower ends of the pterygoid process of the sphenoid, seen from 



the oral surface (the hard palate) (-]-). 



leading to the infraorbital foramen, is situated in the floor of the orbit. It commences at 

 the inner end of the inferior orbital fissure as the infraorbital groove (Fig. 99). 



9. The frontal and supraorbital foramina, situated in the supraorbital margin. 



The orbit contains the following depressions or fossae : 



1. The fossa for the lachrymal gland (Fig. 69), on the frontal bone beneath the outer 

 portion of the supraorbital margin. 



2. The trochlear depression (Fig. 68), also on the frontal bone, where it passes into the 

 inner wall of the orbit, for the attachment of the pulley of the superior oblique muscle. 



3. The fossa for the lachrymal sac (Fig. 99), situated in the inner wall of the orbit between 

 the anterior lachrymal crest of the frontal process of the maxilla and the posterior lachrymal 

 crest of the lachrymal bone. 



The only groove in the orbit is the infraorbital groove (Fig. 98), upon the orbital surface 

 of the body of the maxilla. 



There are several projections into the orbital cavity. These are the anterior and posterior 

 lachrymal crests which form the fossa for the lachrymal sac, and a bony spine upon the greater 

 wing of the sphenoid bone near the outer margin of the superior orbital fissure, the spine for 

 the external rectus muscle (Fig. 99). The frontal bone occasionally presents a trochlear spine 

 alongside of the trochlear depression. 



The orbital walls vary greatly in their thickness. The thinnest wall is the inner one, both in the region of the 

 lamina papyracea of the ethmoid bone and also in that of the lachrymal bone, the latter bone even being sometimes 

 defective. The roof of the orbit not infrequently contains a portion of the frontal sinus, in which case it is hollow. 

 The outer wall is usually the thickest. 



THE NASAL CAVITY. 



The bony nasal cavity (Figs. 99, 101, and 102) is subdivided into two symmetrical nasal fossae 

 by the nasal septum, which is frequently oblique and not exactly in the median sagittal plane. 

 The cavity is highest just behind the anterior nares and gradually becomes lower toward the 

 posterior nares, and nine of the bones of the skull — the nasal, frontal, ethmoid, sphenoid, maxilla, 

 palate, inferior turbinated, lachrymal, and vomer — take part in its formation. In each nasal 

 fossa there may be recognized a roof, a floor, an internal wall, and an external wall. The anterior 

 opening of the two bony nasal fossae is known as the aperlura piriformis (anterior nares), while 

 the posterior opening of each is the choana. The former (Figs. 37 and ^8) is bounded by the 

 nasal bones and by the frontal processes and bodies of the maxilla, while each choana (posterior 

 naris) (Figs. 41 and 42) is bounded by the palate bone, the internal plate of the pterygoid 

 process, and the body of the sphenoid bone. The roof of the nasal cavity is formed anteriorly 

 by the two nasal bones and by the nasal portions of the frontal bones, in the middle by the 



