56 PHYSIOLOGY. 



inches in length. The duct opens on the side of the lingual fraenum. 

 The blood-vessels are branches of the facial and lingual. The nerves 

 are those from the submaxillary ganglion, and through this, from the 

 chorda tympani. The sympathetic also supplies this gland. 



The sublingual gland rests on the floor of the mouth and is seen 

 beneath the side of the tongue as a ridge. It has a half-dozen ducts 

 called the Rivinian, which open on the ridge that marks the position 

 of the gland on the side of the fraenum. 



STRUCTURE OF THE SALIVARY GLANDS. 



These glands are of the compound racemose variety. The alveo- 

 lus has a duct ending in it. The alveoli are united by the blood- 

 vessels and a small amount of loose connective tissue with lobules. 

 The alveoli of the salivary glands are divided into two classes, accord- 

 ing to the kind of secretion, one kind giving a secretion containing 

 mucin, and the other kind secreting a more watery fluid containing a 

 large amount of serum-albumin; hence the alveoli are mucous or 

 serous. The sublingual chiefly secretes mucus, the parotid chiefly 

 serum-albumin. The submaxillary secretes both kinds. In most of 

 the alveoli of the glands, there are found cells of a kind differing from 

 the mucin-cells, as in the submaxillary of the cat, where they form 

 an almost complete outer layer, next to the base membrane and inclos- 

 ing the mucin-cells, and are called "marginal cells." In the dog's 

 submaxillary they are seen only as semilunar masses known as the 

 half-moons of Gianuzzi. The lymphatics lie closer to the alveoli than 

 the capillary network of blood-vessels. The lymphatics begin in the 

 form of lacunae, between and around the alveoli. The nerves pierce 

 the basement membrane and arborize between and around the cells 

 of the alveoli. 



PHARYNX. 



The pharynx is a funnel-like cavity running from the under sur- 

 face of the skull down to the level of the flfth cervical vertebra, where 

 it ends in the oesophagus. There are 7 openings communicating with 

 it: the 2 posterior nares, the 2 Eustachian tubes, the mouth, the 

 larynx, and the oesophagus. The walls of the pharynx are musculo- 

 membranous. The interior is lined with a soft, red, mucous mem- 

 brane containing many glands. Squamous cells are the chief variety 

 of epithelium lining the mucous membrane. Next is a fibrous coat, 

 then a muscular coat, and outside of this a fibrous investment which 

 attaches it to the skull. The muscular coat includes the superior, 



