48 TOPOGRAPHIC AND APPLIED ANATOMY. 



the sphenoidal fissure. The most superficial nerve, and the one first exposed beneath the perior- 

 bita after chiseling open the orbit from the frontal cavity, is the frontal branch (upon the levator 

 palpebrae superioris) of the ophthalmic nerve, which has already been mentioned in the section 

 upon the scalp. The second branch of the ophthalmic nerve, the lachrymal (to the lachrymal 

 gland), is also superficial, while the third branch, the nasal nerve, passes internally between the 

 posterior portion of the superior rectus muscle and the optic nerve, gives off the long ciliary nerves 

 to the eyeball, and divides into the infratrochlear, the anterior ethmoidal, and the posterior 

 ethmoidal nerves. The trochlear nerve runs along the upper and inner portion of the orbit to the 

 superior oblique muscle. The abducent nerve, situated to the outer side of the optic nerve in 

 association with the nasal nerve, passes to the external rectus muscle. All of the remaining 

 ocular muscles are supplied by the oculomotor nerve, which divides before it enters the orbit 

 into a superior division, for the levator palpebrae superioris and the superior rectus, and into an 

 inferior division, for the internal rectus, the inferior rectus, and the inferior oblique. 



The small ciliary ganglion is situated in the posterior portion of the orbit external to the optic 

 nerve. Its roots and branches should be reviewed in a systematic anatomy. We also find within 

 the orbit, but outside of the periorbita, two branches of the superior maxillary division of the 

 trifacial, the small temporomalar nerve and the important infraorbital nerve. 



THE NASAL CAVITY. 



The nasal cavities are paired structures, the bony framework of which is open anteriorly at 

 the apertura pyrijormis (anterior nares) and posteriorly at the choana (posterior nares). The 

 apertura pyriformis is formed by the lower margin of the nasal bone and by the margin which 

 separates the facial from the nasal surface of the superior maxilla. The choanse are bounded by 

 the posterior edge of the vomer, by the pterygoid process of the sphenoid, and by the horizontal 

 plate of the palate bone. 



The roof of the bony fossa is formed by the nasal bone, by the thin cribriform plate of the 

 ethmoid transmitting the olfactory filaments, and posteriorly by the body of the sphenoid, whose 

 anterior as well as inferior surfaces project into the nasal cavity, diminishing the vertical diameter 

 of this cavity to the extent of the vertical diameter of the body of the sphenoid. The sphenoid 

 body contains the two sphenoidal sinuses. A pointed instrument may be driven into the brain 

 from the nasal cavity, through the cribriform plate of the ethmoid, without using a great deal of 

 force. 



The floor o] the nasal fossa, when the individual looks straight ahead, slopes gently down- 

 ward and backward and is slightly concave from side to side. It consists of the palatal process 

 of the superior maxilla and of the horizontal plate of the palate bone, which are united in the 

 transverse palatine suture. 



The inner wall, or the vertical septum separating the two nasal fossas, is usually deflected 

 more or less to one side; this displacement is occasionally so marked that the affected nasal 

 cavity is greatly narrowed or even obliterated. These deflections of the septum are due to dis- 

 turbances of growth, and are to be differentiated from those occasionally produced by tumors, 

 which grow into the nasal fossa from the base of the skull through the cribriform plate of the 



