396 TEE DIGESTIVE APPARATUS IN MAMMALIA. 



of a tube — as in the kidney ; or a vesicle, as is seen in the pancreas ; or deposited 

 without any order in the meshes of a plexus of canaliculi, as occurs in the liver. 



The conglomerate glands are provided with a common excretory duct, that 

 commences in their mass by a great number of arborescent ramifications. The 

 walls of this duct are composed of an elastic, and sometimes contractile, connective 

 tissue membrane, covered on its inner face by an epithelium, which may or may 

 not be of the same character as that of the gland. 



For a long time there have been classed as glands certain organs without 

 excretory ducts, and having only analogies to glands. The majority of these 

 belong to the lymphatic apparatus, and will be considered hereafter ; but it 

 may be mentioned here that they are all composed of masses of cells ; some are 

 small and simple — these are the closed follicles, solitary or agminated, and dis- 

 persed beneath the intestinal mucous membrane ; the others are more complex 

 and voluminous, and form lymphatic glands. 



To the vascular system, but more particularly to the lymphatic apparatus, 

 are annexed other glandiform organs, the fundamental structure of which, 

 analogous in principle to that of the lymphatic glands, is, nevertheless, dis- 

 tinguished from them by certain peculiarities — such are the spleen, thymus 

 gland, and thyroid body. 



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 a descrip- 

 tion of the digestive apparatus in Mammals. 



CHAPTER II. 



THE DIGESTIVE APPARATUS 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 (eso- 

 phagus. 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. 



Aeticle 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 having 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 cheeks, 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 a 

 portion of its inferior face and border — of the isthmus of the fauces, or posterior 

 opening of the mouth. 6. The dental arches fixed on each jaw. 



