330 TEE DIGESTIVE APPARATUS IN MAMMALIA. 



For a long time there have been classed as glands certain organs such 

 as the spleen and thymus body without excretory ducts, and having only 

 remote analogies to glands. The function of these organs is but little known ; 

 though as they are always abundantly supplied with blood-vessels, and as 

 they are therefore believed to have connections with the vascular system, 

 they have been named vascular blood-glands. 



This is the limit to which the generalities relating to the viscera that 

 form the object of splanchnology must be confined. We will now pass to 

 the description of the digestive apparatus in mammals, and which consists, 

 as mentioned above, of a series of enlarged or tubuliform cavities, to which 

 are annexed the glandular organs designated the liver pancreas, and spleen. 



CHAPTER II. 



THE DIGESTIVE APPAKATUS IN MAMMALIA. 



WE will study, successively : 1, The preparatory organs, which include 

 the mouth, the salivary glands annexed to that cavity, the pharynx, and 

 the oesophagus ; 2, The essential organs, comprising the stomach and intestine, 

 and their annexes the liver, pancreas, and spleen ; with the abdominal cavity, 

 which contains and protects these organs. 



ARTICLE I. PREPARATORY ORGANS OF THE DIGESTIVE APPARATUS. 



THE MOUTH. 



The mouth, the first vestibule of the alimentary canal, is a cavity 

 situated between the two jaws, elongated in the direction of the larger axis 

 of the head, and pierced by two openings : an anterior, for the introduction 

 of food, and a posterior, by which the aliment passes into the pharynx. 



The mouth should be studied in six principal regions : 1, The lips, 

 which circumscribe its anterior opening ; 2, The cheeJcs, forming its lateral 

 walls ; 3, The palate, which constitutes its roof or superior wall ; 4, The 

 tongue, a muscular appendage, occupying its inferior wall ; 5, The soft palate 

 (velum pendulum palati), a membranous partition situated at the posterior 

 extremity of the buccal cavity, which it separates from the pharynx, and 

 concurs in the formation, by its inferior border, of the isthmus of the fauces, 

 or posterior opening of the mouth ; 6, The dental arches fixed on each jaw. 



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

 examination of the mouth in general. 



Preparation. The whole of the mouth ought to be examined in an antero-posterior 

 and vertical section of the head, as in figure 152. 



1. The Lips. (Fig. 110.) 



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

 below, the anterior opening of the mouth, which they circumscribe. There 

 is, consequently, a SUPERIOR and an INFERIOR I/IP, 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 face is convex, and presents, on the median line : in the 

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



