1542 HUMAN ANATOMY. 



deeper parts and in the scanty submucous tissue. They are named labial, buccal, 

 and ?nolaf\ according to their situation. The labial glands are gathered into a series 

 of groups near the inner border of the hps, the buccal gla7ids are smaller and scattered, 

 and the w^/ar^/a^z^j- are well-defined groups opposite the molar teeth. The duct 

 of the parotid gland {q.v.) opens into the vestibule, the space between the lips and 

 cheeks externally, and the teeth and alveolar processes internally. Separating the 

 vestibular space from that of the mouth proper behind the alveolar processes is a 

 prominent fold of mucous membrane over the pterygo-maxillary ligament. This fold 

 appears at the inner side of the last upper molar and runs downward and outward to 

 that of the lower. The space behind the teeth when the mouth is closed is small, 

 but a tube some 5 mm. in diameter can be passed through it. 



Vessels. — The arteries supplying the lips, which are very vascular, are chiefly 

 the coronary branches of the facial arteries, each of which forms an arch meeting its 

 fellow in each lip. The vessel lies between the muscles and the glands of the mucous 

 membrane, nearly opposite the line of junction of the latter and the intermediate por- 

 tion. The pulsation is easily felt through the mycous membrane. The vei?is, less 

 regular, lie on the outer side of the muscles. The lymphatics empty into the glands 

 at the angle of the jaw, excepting those near the median line of the lower lip, which 

 run into the suprahyoid glands. 



Nerves. — The mucous membrane of the cheek is supplied by the buccal branch 

 of the inferior maxillary division of the fifth cranial nerve, the lips by the terminal 

 branches of its second and third divisions. 



THE TEETH. 



In form the teeth present three parts, — the body or crown, coated with enamel ; a 

 somewhat constricted part, the neck, covered by the gums ; and the root ox fang, 

 which, covered by the cementum, is fixed in the socket. The greater part of the 

 tooth is composed of the dentine and surrounds the pulp-cavity , to which minute 

 openings in the root or roots transmit vessels and nerves. 



The shape of the crowns is the basis of classification. Thus, in the front teeth 

 the crown is flattened so as to have a chisel-like shape, adapted to cutting, hence 

 these are termed incisors ; the canine teeth have the crown forming a single point or 

 cusp ; the bicuspids have two, and the multictispids , or molars, several cusps. The 

 crowns of all the teeth may be considered as modifications of a simple cone, or as 

 combinations of several cones. ^ 



In man the teeth come in two sets, the temporary or milk and t\\Q permanent 

 teeth ; the total number of the former is twenty, that of the latter thirty-two. The 

 number and arrangement of the teeth of any animal is expressed in its dental formula ; 

 this for man, for the left half of the mouth, may be written as follows : 



Temporary Teeth : i^ c\ m^ ( = ^'X 2^= 20 ) . 



21 2 V 5 / 



Permanent Teeth : /? rl bi^ m^ ( = -'X 2=: X2\. 

 2 I 2 3V 8^ ^ J 



It will thus be seen that in the milk-teeth there are no bicuspids and one molar less. 



Since the typical mammalian dental formula is z_ c^ bi- m±, it may be assumed 



^ . . 3143 



that m man three pairs have been suppressed. These suppressed teeth are occasion- 

 ally represented by supernumerary ones ; from the position of the latter it is probable 

 that the missing teeth are the second incisors and the first and fourth bicuspids. 



To avoid confusion in the nomenclature of the teeth from the curve of the jaws, 

 it is customary to speak of the labial and lingual surfaces of the incisors and canines, 

 and of \.\\e^ facial , or biiccal, and lingual suriaces of the bicuspids and molars. The 

 sides against the other teeth are often called the median and distal, supposing the 

 teeth to be implanted in a straight transverse line. This is not satisfactory in all 



'See Homologies, pag;e 1566. 



