THE MOUTH. 331 



inferior lip, and altogether posteriorly, the single prominence named the 

 tuft of the chin. This face, formed by the skin, is garnished with fine, short 

 hairs, amongst which may be remarked long, coarse bristles, whose bulbs 

 are implanted perpendicularly in the integument, and pass beyond its deep 

 surface, to be lodged in the subjacent muscular tissue. These pilous 

 tentacles ought to be considered as veritable tactile organs, as several 

 sensitive nervous twigs penetrate to the bottom of their follicles. 



The internal face, constituted by the buccal mucous membrane, and 

 moulded on the incisor teeth, is concave, smooth, rose-coloured, and often 

 stained with black spots. In the superior lip, particularly, may be remarked 

 numerous orifices opening on the summits of three small papillae ; these are 

 the openings of the excretory canals by which the labial glands discharge 

 their fluid into the interior of the mouth. 



The free border, thin and sharp, bears the line of demarcation, which 

 separates the two teguments. 



The adherent border is limited, in the buccal cavity, by a groove formed 

 by the mucous membrane in its passage from the dental arches to the inner 

 side of the lips. Beyond the mouth it is not indicated by any peculiarity 

 of structure or arrangement, the skin being continued directly from the 

 neighbouring parts on the lips. 



The commissures mark, on each side, the point of reunion between the 

 free border of the two lips. They are rounded in Solipeds, and offer 

 nothing remarkable otherwise. 



STRUCTURE. Each lip is composed of two tegumentary layers : one 

 cutaneous, the other mucous, between which is found muscular tissue and 

 glands, and the general elements of every organisation vessels and nerves. 



1. Tegumentary layers. Thes&m adheres closely to the subjacent tissues, 

 and apart from the characters already indicated, there is nothing more to be 

 said at present, with regard to its disposition, as it will be studied more 

 completely with the organs of sense. With regard to the mucous membrane, 

 it may be remarked that its derm is thick and dense, and lies on a layer of 

 salivary glands; that it is provided with simple conical papillae, and is 

 covered by stratified pavement epithelium. (It is sometimes streaked with 

 pigment.) 



2. Muscles. These are: the labial or orbicularis, the sphincter of the 

 buccal aperture, and common to the two lips ; in the upper lip, the aponeu- 

 rotic expansion of the supermaxillo-labialis, the musculo-fibrous tissue 

 which separates this expansion from the cutaneous integument, and the 

 terminal insertion of the supernasalis-labialis and the great supermaxillo- 

 nasalis ; in the inferior lip, the tuft of the chin and its suspensory muscles 

 the posterior intermediates (levatores menti). All these muscles having been 

 studied in detail in the Myology (page 217), there is no necessity for their 

 being again described. 



3. Labial glandules. These form an almost continuous layer between 

 the mucous membrane and the labial muscle. They are little secretory 

 organs, similar in their structure and uses to the salivary glands, and will 

 be described when these come under notice. 



4. Vessels and nerves. The blood is carried to the lips by the palato- 

 labial, and the superior and inferior coronary arteries. It is returned to the 

 heart by the satellite veins of the two last vessels. The lymphatics are very 

 numerous, and pass to the glands between the branches of the lower ja\v. 

 The nerves are of two kinds : the motor, which are given off from the facial 

 nerve, and are distributed in the muscular tissue of the lips to cause its 



