150 STUDENTS HISTOLOGY 



THE (ESOPHAGUS 



Beginning with the oesophagus, we encounter an arrangement 

 of layers of muscle and fibrous tissue, constituting the walls of a 

 tube, lined with mucous membrane, which continues throughout 

 the rest of the alimentary canal. The part of the tube below the 

 oesophagus possesses in addition a serous covering, derived from 

 the peritoneum, on the outside. 



The walls of the oesophagus are made of the following layers 

 from within out : Mucous, muscularis mucosae, submucous, mus- 

 cular, and fibrous. 



The mucous membrane is covered with stratified squamous epi- 

 thelium, resting on a layer of connective tissue, which presents 

 minute papillae. 



The muscularis mucosce consists of a small amount of unstri- 

 ated muscle, lying below the mucous membrane. The fibers run 

 longitudinally. 



The submucous layer is composed of loose connective tissue, 

 which accommodates itself to the contractions of the muscular 

 portion, and permits the mucous membrane to be thrown into 

 folds. The blood-vessels, lymphatics, and nerves are distributed 

 through the submucous layer to the other structures. Mucous 

 glands are found in the submucous tissue. Their contents reach 

 the surface by means of ducts. 



The muscular coat consists of an inner layer, fibers of which run 

 in a circular direction about the oesophagus, and of an outer longi- 

 tudinal layer. In the upper third of the oesophagus the muscle is 

 striated, in the lower third it is unstriated, and in the middle 

 third the two kinds are found mixed. 



PRACTICAL DEMONSTRATIONS 



Tke tongue, taste-buds, tonsils, and oesophagus should be studied in this 

 connection. The taste-buds may easily be obtained in sections of the papilla? 

 foliatse of the rabbit's tongue. The tongue itself should be secured from one 

 of the lower animals, and sections that pass through the papilla should be 

 sketched. The papillae make beautiful objects in stained sections. The ton- 

 sils of a human subject should be used. The sections of the tonsil must be 

 very thin. The oesophagus may be taken from one of the lower animals. 

 These tissues may be hardened in alcohol, or, better, in Orth's mixture of 

 Miiller's fluid and formaldehyde. They may be cut, stained with hsematoxylin 

 and eosin, and mounted in the usual manner. 



