CHAP. XXIII.] THE LIPS AND TONGUE. 163 



tive apparatus considered in this chapter. The lips are moved by 

 about twenty muscles, and are capable of grasping and retaining the 

 food placed within them, and of aiding in the subsequent motions 

 which it is made to undergo in the mouth. Their employment in 

 articulation will be spoken of in another place. 



The lips and the tongue undergo a variety of modifications in the animal 

 series, with reference to the function of prehension ; among these may be 

 enumerated the enlarged, pendulous, and very moveable lips of the ruminants 

 and solipeds, and of some monkeys. Man uses his lips in suction, as do the 

 young of all mammalia, at the breast. Among fishes, the cyclostomatous 

 group (as the lamprey) have a suction power of a similar kind, their circular 

 mouth being surrounded and supported by a ring of cartilage, and furnished 

 with appropriate muscles for producing adhesion to surfaces to which it is 

 applied. In birds, the lips are modified so as to form the bill, which is always 

 the prehensile organ in that class. 



The tongue is used by man and animals in suction, somewhat as 

 a piston, being drawn within the mouth so as to exhaust the anterior 

 part of that cavity, and allow fluids to enter by the atmospheric 



glands of both. In the female, however, there is an exception in the case of 

 the ovaries, as will be explained in a subsequent page. 



Penetrating into all the recesses of the mucous system, and forming its chief 

 bulk, we find nucleated particles, arranged as a layer, and developed in succession, 

 in such a manner that the old ones disappear, while others advance from below. 

 An epithelium is not peculiar to the mucous system, but is met with also on se- 

 rous membranes, and on the walls of the blood and lymphatic vessels, as well as 

 elsewhere ; but it is distinguished here by its external position as regards other 

 textures, so as to be capable of passing from the body, or to be exposed to the 

 contact of foreign substances. The particles of this epithelium are very differ- 

 ent in different parts, and may be divided into scaly, columnar, glandular, and 

 ciliated. The scaly variety is seen on the skin, and in the alimentary tract as 

 low as the stomach, as well as in the excretory parts of the genito-urinary tract 

 (see vol. i. pp. 404, 412, 437, etc.). The columnar variety consists of rod-like 

 particles, placed endwise, generally bulged near the centre by the nucleus, and 

 narrowest at the point of attachment. They are met with in the air-passages, 

 on the intestinal villi, in the bile-ducts, and elsewhere. The glandular variety 

 is bulky, its particles rather globular than flat or long, and found in all the 

 glands, the several secretions being essentially the contents or substance of 

 the particles set free. The ciliated particles are columnar or sub-globular in 

 shape, but clothed on their free margin with cilia, as in the examples formerly 

 figured (vol. i. p. 62, and ante, p. 4). They are found chiefly in the respiratory 

 tract, and in parts of the genital tract of the female. The true scaly and 

 glandular varieties of epithelium are never ciliated. See Cyclop. Anat., art. 

 Mucous Membrane. 



The epithelium rests, for the most part, on a layer of membrane, hence 

 termed basement membrane, which, in the best-marked examples, is distinctly 

 homogeneous and transparent, but, in some situations is finely fibrous, and 



M 2 



