THE SALIVARY GLANDS. 433 



6. Teeth. — The teeth are thirty-two in number, sixteen in each jaw. They are distributed 

 in the foUowiug manner: four incisors, two canines, two small molars (bicuspidati), and three 

 large molars (multi-cuspidati). 



The incisors, when viewed in profile or longitudinal section, have a wedge-shape» and their 

 free border is more or less sharp. The canines are irregularly conical; the molars have a 

 multiple fang, and the crown is studded with a variable number of tubercles : two on each 

 small molar and four on the large. In youth, there are only twenty teeth, ten in each jaw. 



The Salivary Glands. 



The salivary glands are secretory organs annexed to the buccal cavity, into 

 which they pour saliva — a recrementitious fluid that softens the food, favours its 

 mastication and deglutition, and has a chemical action upon it after its arrival 

 in the abdominal portion of the digestive tube. 



Though very diversified in form, yet they present in their structure such 

 common characters, that, to obviate recurrence to their organization when 

 speaking of each gland, we will describe them here. 



These glands are composed of a greyish-red or yellow spongy tissue, which is 

 divided into small, rounded, or polyhedral masses, called salivary lobules. These 

 extend in a layer beneath the adherent face of the mucous membrane, and 

 remain isolated from each other, or are agglomerated in a body to form a single 

 gland. In the latter case, they are united by close connective tissue, which 

 covers them as a very thin enveloping membrane, and throws into the lobular 

 interstices lamellar prolongations. 



In studying the organization of one of these lobules, it will be observed that 

 it is made up of many very small secondary lobules, or acini, which are themselves 

 due to the agglomeration of minute elementary vesicles or follicles, the average 

 diameter of which is from 3-5-0^ to i^V^ of an inch; these open into the little 

 canal belonging to each of the secondary lobules, and which again joins those 

 of the other acini of the primary lobule, to form a single duct. 



The minute elementary vesicles or follicles — the ghmdidar nds-de-sac (or 

 ultimate follicles) — are more or less completely filled with delicate cells, transparent 

 or slightly granular. They have for wall a thin amorphous membrane {membrana 

 propria), against which, towards the bottom of the caini, and beneath the glandular 

 epithelium, are cells having half-moon-like forms, a group of which constitutes a 

 mass called the crescent (or lanula) of Gianuzzi (or marginal cells) — example, the 

 submaxillary gland. (They are closely surrounded by a plexus of capillary 

 blood-vessels.) 



"When the salivary lobules remain isolated, this canal — which is designated as 

 excretory, because it carries from the lobule the saUva secreted within the 

 elementary follicles — opens directly into the mouth. But when, on the contrary, 

 they all unite and form a single gland, their excretory canals finally converge 

 into one or more principal ducts, the termination of which, in every case, takes 

 place in the same manner — by opening into the mouth from the summit of a 

 more or less salient tubercle ; this arrangement renders the introduction of 

 particles of food into these excretory orifices somewhat difficult. The fibrous 

 and elastic walls of these ducts are lined by cylindrical epithelium. 



To the fundamental tissue just described must be added arteries, veins, and 

 lymphatics, which convey the materials of secretion and nutrition ; as well as 

 the yierves which regulate the secretory and nutritive acts (excito-secretory and 

 vaso-motor nerves). According to many histologists, the excito-secretory nerves 

 remain between the acini, but others (Pfliiger, Gianuzzi, Paladino) assert that 



