142 ANATOMY OF THE DOMESTIC FOWL 



The Esophagus (Fig. i8, No. 6). Location and Shape. — The 

 esophagus is a musculo-membranous tube, capable of great dis- 

 tension, which extends from the pharynx to the proventriculus 

 (Fig- 35. No. I, and 3). 



The esophagus communicates anteriorly with the pharynx. It 

 extends down the neck, lying supero-lateraUy with regard to the 

 trachea and toward the right side. It enters the thorax above the 

 trachea, and, passing through between the bronchi, terminates into 

 the proventriculus. At the entrance of the thorax and just to the 

 right of .the median line, it expands into the crop which divides it 

 into two portions, designated as the first and the second. The 

 first portion of the esophagus is the longer, the length depending 

 upon the size and kind of fowl. 



Structure. — The wall is composed of four coats, the mucous 

 membrane, the submucosa, the muscular coats, and the fibrous 

 sheath or tunic. The mucous membrane is pale and is covered with 

 stratified squamous epithelium. 



The mucous membrane is loosely attached to the muscular coat 

 by the submucosa. Except during deglutition it hes in longitudinal 

 folds which, obliterate the lumen. Opening from the mucosa are 

 lenticular glands, which may be seen on inflating an esophagus 

 and looking through its transparent walls. 



The muscular coat of the esophagus is divided into two layers, 

 an outer longitudinal and an inner circular layer. 



The outer fibrous sheath connects the esophagus loosely to the 

 surrounding structures. 



Function. — The function of the esophagus is to give passage way 

 for the food from the pharynx to the crop and from the crop to the 

 proventriculus. 



The Crop (Fig.3S, No. 2; Figs. 30 and 31). Location and Shape. — 

 The crop, or ingluvies, saccular in shape, is located at the entrance 

 of the thorax and just to the right of the median line. The first 

 portion of the esophagus empties into the crop superiorly and 

 inferiorly the crop opens into the second portion of the esophagus. 

 Like the esophagus the crop is capable of great distension. 



Structure. — The wall of the crop is composed of four coats, the 

 mucous membrane, submucosa, muscular and the outer fibrous. 



The crop is lined with mucous membrane containing mucous glands 

 . which secrete a mucus to keep the surface moist. The surface of the 

 mucous membrane is covered by stratified squamous epithelium. 



