BLOOD-VESSELS AND NERVES OF THE ORBIT 319 



angle of the orbit it gives off the inferior ophthalmic 

 artery (a. ophthalmica inferior). This vessel passes up- 

 ward and forward on the medial wall of the orbit, giving 

 branches to the eye muscles. It divides into two branches, 

 the frontal artery, which leaves the orbit through the 

 anterior foramen of the supraorbital process, and the 

 lacrimal artery, which passes through the corresponding 

 posterior foramen. The ethmoidal artery, a small branch 

 of the frontal, passes through the minute ethmoidal foramen 

 of the orbital portion of the frontal into the nasal cavity. 



The internal maxillary artery passes forward along the 

 ventral boundary of the orbit, and at the opening of the 

 infraorbital canal gives off a branch, the pterygopalatine 

 artery, continuing as the infraorbital artery. A small 

 branch, the superior dental artery (a. dentalis superior) 

 is given off laterally to the alveoli of the upper teeth. 



The infraorbital artery (a. infraorbitalis) passes through 

 the infraorbital canal to the face. 



The pterygopalatine artery (a. pterygopalatina) divides 

 almost immediately into the anterior palatine artery, 

 which traverses the pterygopalatine canal to the mucous 

 membrane of the hard palate, and the sphenopalatine 

 artery, which enters the nasal cavity by the sphenopalatine 

 foramen. 



(b) The divisions of the third cranial, or oculomotor nerve, 

 supply the eye muscles, with the exception of the obliquus 

 superior, rectus lateralis, and retractor oculi. 



This nerve enters the orbit from the superior orbital fissure in com- 

 pany with certain parts of the trigeminal (see e, f below). The small 

 nerves passing through the middle and posterior sphenoidal foramina of 

 the pterygoid process are the pterygobuccinator and masseterico- 

 tetnporal nerves, branches of the mandibular, passing to the muscles 

 of mastication, 



(c) The fourth cranial, or trochlear nerve (n. trochlearis), is 

 distributed to the obliquus superior muscle. 



(d) The sixth cranial, or abducent nerve (n. abducens), is dis- 

 tributed to the rectus lateralis and to the retractor oculi. 



