42 TOPOGRAPHIC AND APPLIED ANATOMY. 



The relation of the parotid gland to the retromandibular fossa furnishes sufficient explanation 

 for the pain produced by mastication when the gland is inflamed and swollen. Since the parotid 

 extends inward toward the pharynx it will be readily understood that large tumors proceeding 

 from the parotid gland cause dysphagia from compression of the pharynx. The proximity of the 

 external auditory meatus explains the occasional perforation of parotid abscesses into this canal. 



In operative procedures upon the parotid gland it is rather difficult to avoid dividing branches 

 of the facial nerve, the resulting paralysis usually being of a temporary character. It should be 

 remembered that the trunk of the facial nerve enters the parotid gland from above and behind, 

 at a point on a level with the base of the lobule of the ear. In total extirpation of the gland 

 it is scarcely possible to avoid injuring the trunk. In operations penetrating deeply into the 

 retro-mandibular fossa, it is important to remember that the external carotid artery, as well as 

 numerous veins (particularly the temporo-maxillary), are in close relation with, or imbedded in, 

 the median surface of the gland. [The temporo-maxillary vein and the external carotid artery 

 usually traverse the substance of the gland, the vein being superficial to the artery and deeper 

 than the facial nerve. ED.] Still more deeply are found the internal carotid artery and the 

 internal jugular vein. 



THE ORBITAL CAVITY. 



The shape of the bony orbit may be compared to that of a four-sided hollow pyramid, the 

 base being situated at the margin of the orbit and the apex at the optic foramen. [The inner 

 walls are almost parallel; the outer walls if prolonged backward would meet in almost a right 

 angle. The depth of the orbit is from 1 1 to 2 inches. ED.] It should be carefully studied from 

 a skull. 



The upper -wall is formed by the very thin orbital plate of the frontal bone (see Figs, i and 16) 

 and a small posterior portion by the lesser wing of the sphenoid. Externally beneath the zygo- 

 matic (external angular) process is the lachrymal fossa, which lodges the lachrymal gland; 

 internally is a small depression, the fovea trochlearis (occasionally also a spina trochlearis), 

 for the attachment of the pulley of the superior oblique muscle. In the supraorbital margin 

 toward the inner side [near the junction of the inner and middle thirds. ED.] is the supra- 

 orbital notch or joramen for the passage of the nerve and artery of the same name. 



The inner wall is formed by the lachrymal bone, the os planum of the ethmoid, and poste- 

 riorly by a portion of the lateral surface of the body of the sphenoid. Anteriorly is a depression 

 for the lachrymal sac (and duct) (fossa saccilachrymalis), bounded by the inner extremity of the 

 supraorbital margin (crista lachrymalis anterior of the superior maxilla) and by the lachrymal 

 crest of the lachrymal bone (crista lachrymalis posterior) ; from this point a sound may easily be 

 passed downward into the nasal duct which opens into the inferior meatus of the nose. Further 

 posterior on the inner wall [between the os planum of the ethmoid and the orbital plate of the 

 frontal. ED.] are situated the anterior ethmoidal foramen, communicating with the cranial 

 cavity, and the posterior ethmoidal foramen, leading to the posterior ethmoidal cells. 



The lower wall is formed by the orbital surface of the superior maxilla containing the in- 

 fraorbital groove and canal, which terminates anteriorly beneath the lower margin of the orbit at 

 the infraorbital foramen and transmits the artery and nerve of the same name (see Figs, i and 16). 



