Chap, vin.] THE MOUTH. 121 



To this cavity the name is given of the sublingual 

 bursa mucosa. It is constricted in its centre by the 

 framum linguae, and is said to be the seat of mischief 

 in " acute ranula." 



When the mouth is widely opened the pterygo- 

 maxillary ligament can be readily seen and felt 

 beneath the mucous membrane. It appeal's as a 

 prominent fold running obliquely downwards behind 

 the last molar teeth. A little below and in front of 

 the attachment of this ligament to the lower jaw, the 

 gustatory nerve can be felt as it lies close to the bone 

 just below the last molar. This nerve is sometimes 

 divided for the relief of pain in cases of carcinoma 

 of the tongue. Mr. Moore's method of dividing it is 

 as follows : " He cuts the nerve about half an inch 

 from the last molar tooth, at a point where it crosses 

 an imaginary line drawn from that tooth to the angle 

 of the jaw. He enters the point of the knife nearly 

 three-quarters of an inch behind and below the tooth, 

 presses it down to the bone, and cuts towards the 

 tooth" (Stimson). This nerve, as it lies against the 

 bone, has been crushed by the slipping of the forceps 

 in the clumsy extraction of the lower molar teeth. 



The coronoid process of the lower jaw can be 

 easily felt through the mouth, and is especially distinct 

 when that bone is dislocated. It may be noted that 

 a fair space exists between the last molar tooth and 

 the ramus of the inferior maxilla, through which a 

 patient may be fed by a tube in cases of trismus or 

 anchylosis of the jaw. 



A congenital dermoid cyst is sometimes found in 

 the floor of the mouth between the tongue and the 

 lower jaw. Such cysts have been supposed to be due 

 to the imperfect closure of the first branchial cleft, the 

 cleft immediately behind the first branchial arch, 

 about which the lower jaw is developed. 



The gums are dense, firm, and very vascular. In 



