480 THE xVNATOMY OF THE HORSE 



ANATOMY OF THE SALIVARY GLANDS, 

 PHARYNX, CESOPHAGUS, AND STOMACH 



The salivary glands are grouped around the jaw, three on each side^ 

 and are named the parotid, submaxillary, and sublingual glands. 



The parotid (so named from its proximity to the ear, irapa, near ; oSs, 

 coTos, the ear) is the largest of the three, and lies in the space between the 

 ramus of the lower jaw and the petrous part of the temporal bone, covered 

 by the parotido-auricularis muscle (see Muscles, Fig. 60). It is enveloped 

 in a case of dense cellular membrane, being itself made up of a number of 

 little lobes, each of which has an investment continuous with the external 

 one. The lobes have each an excretory duct, and these unite together like 

 the stalks of a grape, to form one single duct, which passes along the inner 

 part of the angle of the jaw, along the border of the masseter, piercing the 

 mucous membrane of the mouth opposite the second molar tooth. The 

 SUBMAXILLARY GLAND lies within and before the angle of the jaw, and is of 

 the same structure as the parotid. Its duct passes forward by the side of 

 the root of the tongue, and opens on the side of the froenum. The sublin- 

 gual GLAND is the smallest of the three, and is situated between the middle 

 of the tongue and the lower jaw. Its ducts, which are several in number, 

 open on the side of the froenum of the tongue, close to the oi'ifice of the 

 submaxillary gland. The saliva secreted by these glands contains various 

 saline and earthy matters identical with those of the blood, and a peculiar 

 substance called |;^?/a?me, which is the ferment used in the digestive 

 process. The earthy phosphates in the saliva collect around the teeth, 

 being held together by animal matter, and forming what is known as tartar. 



The pharynx and ceisophagus receive the food from the back of the 

 mouth and convey it to the stomach. The former is a funnel-shaped bag, 

 lined with mucous membrane, and covered by the three constrictors of the 

 pharynx, which suspend it to the os hyoides and palate bones. Posteriorly 

 it lies close to the spine, being only separated by a thin layer of muscles 

 (see anterior ccrvico-occipital region). Anteriorly and superiorly it opens 

 into the mouth and nasal cavities, from which it is separated by the soft 

 palate and epiglottis. Posteriorly and superiorly the eustachian tubes open 

 into it bell-mouthed ; and inferiorly it contracts to connect itself with the 

 oesophagus. The velum-palati is so arranged as to act as a valve in 

 preventing the entrance of air into the larynx through the mouth, but in 

 the act of coughing the latter is convulsively drawn down, and the valve 

 ceases to cover its orifice, so that forciljle expiration can then be effected. 



The cesophagus commences where the pharynx ends, being at first 

 placed behind the larynx and in front of the cervical vertebrae. It soon 

 inclines to the left, where for several inches the passage of a bolus may 

 be observed in the living horse, again ascending and passing into the 

 thorax above it. On reaching the crura of the diaphragm it passes 

 through the opening made for it by the decussation of their fibres (see 

 Diaphragm), and is connected with the stomach about the centre of its 

 anterior curve. Throughout this course it has a muscular coat, composed 

 of striped fibres at its commencement, but afterwards they are unstriped. 

 It is lined by mucous membrane, which is very thick and white. 



