Chap, viz.] THE LOWER JAW. 99 



2. In clearing the outer surface the following 

 parts are dissected back : Levator menti, the two 

 depressor muscles, buccinator, masseter (crossed by 

 part of parotid gland, transverse facial vessels, facial 

 nerve and Stenson's duct), masseteric vessels and nerve, 

 temporal muscle. 



3. In clearing the inner surface : Digastric, genio- 

 hyoid, genio-hyo-glossus, and mylo-hyoid muscles, a 

 few fibres of superior constrictor, internal pterygoid 

 muscle, inferior dental artery and nerve, mylo-hyoid 

 vessels and nerve, internal lateral ligament, rest of 

 insertion of temporal muscle, mucous membrane. 



Parts in risk of being damaged. The facial nerve, 

 if the posterior vertical incision be carried too high up. 

 The internal maxillary artery, temporo-maxillary vein, 

 auriculo-temporal nerve (structures all closely related 

 to the jaw condyle), external carotid artery, lingual 

 nerve, the parotid, submaxillary, and sublingual glands. 

 After subperiosteal resection the entire bone has been 

 reproduced. 



The lower jaw may be entirely absent, or may be 

 of dwarfed dimensions, or be incompletely formed. 

 These conditions are congenital, and depend upon 

 defective development of the maxillary part of the 

 first branchial arch. They are often associated with 

 branchial fistulse, supernumerary ears, macrostoma, 

 and like congenital malformations. 



With regard to the nerves connected with the 

 jaws little need be said. The upper teeth are supplied 

 by the second division of the fifth, the lower by the 

 third. Some remarkable nerve disturbances have 

 followed, by reflex action, upon irritation of the 

 dental nerves. Thus cases of strabismus, temporary 

 blindness, 'and- T .v?y- neck haVe" beet reported- 0,3 due 

 to the ireitali'^iT' of carious teeth.- - Hilfoa" gives 

 the case of a man who was much troubled by a 

 carious *xk>th in t~h& lower jaw (st^plred i>y the third 



