TEE MOUTH. 397 



We will study each of these regions in particular, before passing to the 

 examination of the mouth in general. 



Prepariition.— The whole of the rnoutli ouglit to be examined in an antero-posterior and 

 vertical eectiou of the head (see description of the soft palate). 



L The Lips (Fig. 168). 



These are two membranous movable folds, placed one above the other below 

 the anterior opening of tliu mouth, which they circumscribe. There is, con- 

 secjuently, a superior and an inferior lip, united at each side by a commissure. 



Each lip offers for study an external and internal face, and a free and an 

 adherent border. 



The external surface is convex, and presents, on the median line : in the upper 

 lip, a slight projection which divides it into two lateral lobes ; in the inferior lip, 

 and altogether posteriorly, the single prominence named the ti/ft of ilie chin'. 

 This face, formed by the skin, is garnished with line, short hairs, amongst which 

 may be remarked long, coarse bristles, the roots of which are implanted per- 

 pendicularly in the integument, and pass beyond its deep surface, to be lodo-ed 

 in the subjacent muscular tissue. These pilous tentacles ought to be considered 

 as real tactile organs, because several sensitive nerve-filaments penetrate to the 

 bottom of their follicles, and they have a very remarkable vascularization. 



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

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

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

 nimieroiis 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//w bonier, thin and sharp, shows the line of demarcation that separates 

 the two teguments. 



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

 the mucous membrane in passing from the incisor arches to the inner side x)i 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 union between the free 

 borders 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 organization — vessels and r\,erves. 



1. Tegumentary layers. — The skin 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 mucotis membrane, it may be 

 remarked that its dermis is thick and dense, and lies on a layer of sahvary 

 glands ; it is provided with simple conical papillae, and is covered by stratified 

 tesselated epithelium. (It is sometimes streaked with pigment.) 



2. Muscles. — These are : the labialis or orbicularis oris — the sphincter of the 

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

 expansion of the levator labii superioris propriu^, the musculo-fibrous tissue which 



28 



