C. THE (ESOPHAGUS, BY E. KLEIN. 537 



phagus itself. The muscular layer of the mucosa is equal in thick- 

 ness to that of the ossophagus, and is partially separable into an 

 internal circular, and an external longitudinal layer. 



Hasse* found no glands in the cervical portion of the oesophagus nor 

 in the crop of pigeons, but in the thoracic portion flask-shaped glands 

 appeared, with a long narrow neck, and an internal lining of tesse- 

 lated epithelium. In incubating pigeons he observed a remarkable 

 thickening at the sides of the crop, due to a growth of epithelial 

 cells filled with oil- drops, and resembling those in the milk follicles 

 of Mammals. 



In the Newt and Frog the mucous membrane of the oral cavity 

 behind the tongue passes directly into the mucous membrane of the 

 intestinal tract, which has now become converted into a complete 

 closed tube. 



The oesophagus of the Triton consists of an epithelium, a mucous 

 layer, an external muscular layer, and an investing fibrous membrane. 

 The epithelium, like that of the oral cavity, is columnar. The 

 several cells are conical, with the narrow end more or less prolonged ; 

 whilst the base, directed towards the free surface, is beset with long 

 cilia. Their shape may either be simply conical or strongly ventricose 

 near the surface, and then, becoming suddenly attenuated, send a 

 long process into the deeper-lying parts ; or they may exhibit, when 

 examined in the fresh state, a nucleated swelling in this process. 

 Between the penetrating processes of the superficial cells fusiform 

 cells are interposed, and between these again are here and there 

 spheroidal cells with relatively large nuclei. In transverse sections of 

 the longitudinal folds of the mucous membrane the penetrating pro- 

 cesses of the conical ciliated cells are not directed perpendicularly 

 from the surface, but are curved at their extremities. Hence in many 

 parts these processes appear to be continuous with the elements of the 

 mucous membrane. The mucous membrane consists of broad fas- 

 ciculi of connective tissue, which present a looser texture toward the 

 external muscular layer, and there form larger meshes, whilst nearer 

 the epithelium the tissue is more compact. Fasciculi of connective 

 tissue penetrate perpendicularly to the surface between the fasciculi of 

 the external muscular layer, decussating once or twice at their en- 

 trance into the mucous membrane, and thus forming numerous spaces 



* C. Hasse, Ueber den (Esophagus der Tauben, etc., "On the (Esophagus 

 of the Pigeon ; " Henle and Pfeuflfer's Zeitschrtft, 3. Heine, Band xxiii., 

 p. 101. 





