i 



THE DIGESTIVE TRACT. 593 



between the glosso-palateal and pharyngo-palateal folds. The 

 tonsils vary greatly in size ; sometimes the lymph-follicles which 

 build them up are scanty, at other times numerous. From the 

 covering mucosa a number of depressions are formed, similar 

 to those of the lymph-follicles on the base of the tongue. These 

 depressions in the tonsil may have several lateral elongations 

 uniting with a central cleft, the so-called crypts of the tonsil. In 

 the cavities a viscid, cheesy mass is often formed, which is not 

 infrequently the seat of a calcareous deposition. The mass 

 proves upon examination to be composed of leptothrix (E. Grim- 

 ing), a fungus which is a normal occurrence in all furrows of the 

 oral cavity, especially those between the gums and the teeth. In 

 the mucosa covering the tonsils, acinous mucous glands are 

 present. Hyperplastic tonsils do not histologically differ from 

 normal lymph-ganglia, with numerous follicles. 



In various situations in the wall of the pharynx lymph-tissue 

 is found, and on the roof the aggregation of this tissue bears the 

 superfluous name of the pharyngeal tonsil. 



The oesophagus in rest appears completely closed by large folds 

 of the mucosa, which is composed of a loose fibrous connective 

 tissue, and admits of a high degree of extension. Along the 

 epithelial cover it shows numerous small papillae, but which are 

 not marked on the surface of the stratified epithelium. The vas- 

 cular supply is very abundant in the layers, directly below the 

 epithelium, but scanty in the portion near the muscle. The 

 muscle in the upper half or two-thirds of the oesophagus is of the 

 striated variety, composed of at least two layers, an outer longi- 

 tudinal and an inner circular, and in some places near the mucosa 

 a second longitudinal or oblique layer is often found. In the 

 oesophagus of the rabbit this is a constant formation. (See Fig. 

 251.) In the lower portions of the oesophagus a gradual transition 

 of the striated into smooth muscle-fibers takes place. In the pos- 

 terior wall, according to Treitz, the striped muscles extend down 

 more deeply than in the anterior, and bundles of these muscles 

 terminate in tendinous formations, which blend with the external 

 fibrous investment. The mucosa of the oesophagus has also 

 independent bundles of smooth muscle-fibers, which are scanty in 

 its upper portions, but form a continuous layer in the thoracic 

 portion (Toldt). 



(4) The Stomach. The mucous layer of the stomach is marked 

 by an abundant glandular apparatus, the so-called gastric tubules 

 or pepsine glands. This mucosa, owing to its attachment to the 

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