234 THE 1/lSCERA. 



Action. Constrictor of the pharynx. 



3. The (Esophagus. The oesophagus is a straight tube, 

 dorsoventrally flat when empty, which extends from the 

 pharynx to the stomach. It has a uniform diameter when 

 moderately dilated of about one centimeter. It lies dorsad of 

 the trachea and against the longus colli muscles (Fig. 72, g'} 

 covering the centra of the cervical vertebrae, until it reaches 

 the caudal end of the thyroid gland (Fig. 96, e) ; then it passes 

 to the left and lies laterodorsad of the trachea until it reaches 

 the bifurcation of the trachea. It there returns to the median 

 line, passes gradually distad, separated from the vertebrae by 

 the aorta, and finally pierces the diaphragm about two centi- 

 meters from the dorsal body wall, and enters the stomach. Its 

 attachment to the diaphragm is loose enough to permit of longi- 

 tudinal motion. In passing through the thoracic cavity it lies 

 in the posterior mediastinum ventrad of the aorta. Its wall 

 consists of a muscular coat, a submucosa, and a mucosa, and 

 its inner surface presents many longitudinal folds. It has no 

 serous covering, its side walls being merely in contact with the 

 halves of the mediastinal septum. 



4. The Stomach. Ventriculus (Fig. 97). The stomach 

 is the widest part of the alimentary canal. It is a pear-shaped 

 sac, the long axis of which is curved nearly into a semicircle. 

 The broad end of the sac lies to the left and dorsad ; here the 

 stomach communicates with the oesophagus (a). The narrowed 

 end extends to the right and lies more ventrad than the other 

 end; it passes here into the duodenum (g}. That portion of 

 the stomach which communicates with the oesophagus is known 

 as the cardiac end (b} ; the opposite is the pyloric end. Owing 

 to the curved form of the stomach above mentioned it is possi- 

 ble to distinguish a concave and a convex side. The concave 

 side is directed craniad and dextrad ; it is called the lesser 

 curvature of the stomach (<:). The longer convex border is 

 directed caudad and to the left; it is called the greater curva- 

 ture (d~). The greater curvature extends to the left, next to 

 the oesophagus, into a prominent convexity known as the 

 fundus (e) of the stomach. 



The stomach lies at the cranial end of the abdominal 



