104 SURGICAL APPLIED ANATOMY. [Chap.vm. 



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 cyst is sometimes found in the floor 

 of the mouth between the tongue and the lower jaw, 

 that contains sebaceous matter and hairs. 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 

 the bleeding that follows the extraction of teeth much 

 of the blood is supplied by them. The gums are 

 particularly affected in mercurial poisoning, and are 

 also especially involved in scurvy. In chronic lead- 

 poisoning a blue line often appears along their margins. 

 This is due to a deposit of lead sulphide in the gum 

 tissues, which is thus derived : Food debris collected 

 about the teeth in decomposing produces hydrogen 

 sulphide, which, acting upon the lead circulating in 

 the blood, produces the deposit. The blue line, there- 

 fore, is said not to occur in those who keep the teeth- 

 clean. 



The tongue. On the under surface of the tongue, 

 less than half an inch from the frsenum, the end of the 

 ranine vein can be seen beneath the mucous membrane. 

 Two elevated and fringed lines of mucous membrane 

 may be seen on the under surface of the organ 

 converging towards its tip. They indicate the position 

 of the ranine artery, which is more deeply placed than 

 the vein, close to which it lies. It is extremely rare 

 for the tongue to be the seat of congenital defect. The 

 author of the able monograph on the tongue in 

 Holmes' " System of Surgery " has discovered only 

 one instance of congenital absence of the organ. 

 Fournier gives a case where the tongue was so much 



