THE PHARYNX — THE (ESOPHAGUS — THE STOMACH 497 



maxillary nerve. It has four or five ducts which open near the last upper cheek 

 tooth; one of them (Ductus glandulse zygomatics major) is almost as large as the 

 parotid duct; the others (Ductus glandulsff zygomatics minores) are small. 



THE PHARYNX (Fig. 434) 



The fornix is narrow. The pharyngeal orifices of the auditive or Eustachian 

 tubes are small and slit-like; the end of the tube causes a rountled projection of the 

 mucous membrane (Torus tubarius). The oesophageal aditus is relatively small 

 and is well defined by a transverse fold of the mucous membrane. The muscles 

 present no marked differential features, but the hyo-pharyngeus muscle is clearh^ 

 divided into a kerato-pharyngeus and a chondro-pharyngeus. 



THE CESOPHAGUS 



The oesophagus is relatively wide and dilatable except at its origin, where there 

 is a constriction termed the isthmus oesophagi. This initial narrowness of the 

 lumen is caused by a prominence of the ventral part of the mucous membrane, 

 underlying which is a thick layer of mucous glands (Fig. 490). The cervical part 

 is at first median and is dorsal to the trachea, but in the posterior part of the neck 

 it lies to the left of the trachea. The thoracic part continues in this position and 

 ventral to the left longus colli to the base of the heart; here it inclines medially, 

 having the aortic arch on its left, and passes back over the bifurcation of the trachea. 

 Continuing backward between the lungs it usually inclines slightly to the left, 

 passes through the hiatus oesophageus, and joins the stomach just to the left of the 

 median plane and ventral to the eleventh or twelfth thoracic vertebra. The 

 muscular tissue is striated and consists mainly of two layers of spiral fibers which 

 cross each other; near the cardia, however, the fibers are longitudinal and circular. 

 There are tubulo-alveolar glands (Gl. oesophagse) in the submucosa throughout. 



THE STOMACH 



The stomach is relatively large. Its capacity in a dog weighing about 40 

 pounds is about six to seven pints. 



Colin estimates the average capacity at about 3 liters (ca. 6H pints), with a range between 

 0.6 and 8 Hters (ca. IM to 17J^ pints). Neumayer gives the capcaity as 100 to 250 c.c. per kilogram 

 of body-weight (ca. 2.7 ounces per pound). The average capacity of the human stomach is esti- 

 mated at 1.2 liters {2}4 pints) — not much more than a third of that of a dog of medium size. 



When full, it is irregularly piriform. The left or cardiac part (Fundus et corpus 

 ventriculi) is large and rounded, while the right or pyloric part (Pars pylorica) is 

 small and cylindrical. When empty, or nearly so, the left sac is strongly contracted; 

 the pyloric part is much less affected by variations in the amount of ingesta. 



The parietal surface of the full stomach is very extensive, strongly convex, 

 and faces partly forward, but largely ventrally and to the left. It is related to the 

 liver, the left part of the diaphragm, and the left and ventral abdominal wall as far 

 back as a transverse plane through the second or third lumbar vertebra. The 

 visceral surface is much less extensive and is considerably flattened ; it faces chiefly 

 dorsally and to the right, and is related to the intestine, pancreas, and left kidney. 



The upper part of the lesser curvature is nearly straight and vertical, but the 

 lower part forms a deep, narrow angle (Incisura angularis), due to the fact that the 

 pyloric part is directed sharply forward and upward. The greater curvature is 

 nearly four times as long as the lesser curvature. In the full stomach it extends 

 considerably behind the left costal arch; ventrally it lies on the abdominal wall 

 about midway between the xiphoid cartilage and the pubis. 

 32 



