72 APPLIED ANATOMY. 



of the jaw, and it is to avoid bringing it too close to the bone that Jacobson advises 

 that the jaw be not twisted outward when disarticulation is being performed. 



The distance between the coronoid process and malar bone varies in different 

 individuals. The process may be displaced by the tumor and thus prevent detachment 

 of the temporal muscle. If so, the process is divided with forceps or saw and removed 

 after the rest of the jaw has been taken away. Injury of the temporomaxillary veins 



Masseter muscle 

 Lingual nerve 



Anterior belly of -^ 



digastric musclr 'X^tfi^-Z^'ii^^lL tJ-*^''^ f""%&^SS&^^~ *- - Muscular branches 



of internal maxil- 

 lary artery 



Inferior alveolar 

 (dental) nerve and 

 artery 



nternal pterygoid 

 muscle 



Duct of submaxillary 

 gland 



^ Facial vein 

 Facial artery 



Sublingual gland 

 FIG. 85. Excision of one-half of the lower jaw, showing the structures exposed, 



may be avoided by not going behind the posterior edge of the ramus, as is also the 

 case with the external carotid artery. Access to the joint may be facilitated by drag- 

 ging upward the parotid gland, which carries with it the facial nerve and parotid duct. 



REGION OF THE EYE. 



The eyeball rests in its socket, which is hollowed out of the soft parts contained 

 in the bony orbit. It is covered in front by the lids, which, as they slide over the 

 eye, are lubricated by the tears. These are secreted by the lachrymal gland at the 

 upper outer portion of the orbit, flow over the eye, and are drained off by the lach- 

 rymal canals and sac to empty into the nose through the lachrymonasal duct. 



The Orbits. The orbits are large four-sided cavities, pyramidal in shape. 

 The orbit in an adult male is about 4 cm. in diameter from side to side, and 3. 5 cm. 

 from above downward. The depth is 4. 5 cm. It is thus seen that the orbit is wider 

 than it is high. On receding into the orbit from its bony edge, the roof arches 

 upward toward the brain to receive -the lachrymal gland, thus making the up-and- 

 down diameter slightly longer than the transverse. 



The rim of the orbit is very strong and not readily broken by injuries. It is 

 formed by the frontal bone above, the malar bone to the outside, the malar and supe- 

 rior maxillary below, and the superior maxillary and frontal to the inside. The 

 inner (medial) walls of the two orbits are parallel, running distinctly anteroposte- 

 riorly. The outer (lateral) walls diverge at an angle of about 45 from the inner ones. 



The outer or lateral edge of the orbit is nearly or quite a centimetre and a half 

 posterior to the inner or medial edge. This fact, together with the divergence of the 

 outer wall, is the reason that, in enucleation of the eye, it is always tilted toward the 

 nose, and the scissors introduced and the nerve cut from the outer side. 



The outer wall of the orbital cavity is formed mainly by the broad flat surface of 

 the greater wing of the sphenoid bone, and is thick and strong. The other three 



