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LESSON XIX. 

 THE DIGESTIVE TRACT. 



(a) Cross-Section of Human Lip. 



Pieces of the lip of a child were hardened in mercuric chloride, 

 stained in Delafield's hsematoxylin, embedded in paraffin, and 

 cross-sectioned. Fix to the slide and mount. 



Study under low power. Observe that the outer sur- 

 face of the lip is covered with a thin epidermis resting on 

 a dermis in which many hair follicles, sebaceous and sweat 

 glands are found. The inner surface of the lip is covered 

 with a mucous membrane consisting of stratified pavement 

 epithelium and a fibrous mucosa. In the submucous 

 tissue, and in the deeper parts of the mucosa, are often 

 found quite large mucous glands which empty on the inner 

 side of the lip. Between the epidermal and mucous sur- 

 faces striped muscle, fibrous, and adipose tissue is found. 

 Often one or more quite large blood vessels and nerve 

 trunks are seen. Sketch under low power. 



(b) Section of the Tongue Showing Filiform 



Papillae. 



The tip of the tongue of a cat was hardened in mercuric 

 chloride, stained in Delafield's hsematoxylin, embedded in paraffin, 

 and longitudinal sections cut. Fix to the slide, and mount in 

 balsam. 



Study under low power. The papilla? are found on 

 the dorsal surface. The mucosa is thrown into conical 

 projections, the primary papillae, on which several second- 

 ary papillae are often seen. The papillae are covered with 

 stratified pavement epithelium, which on the outer surface 

 has a smooth free border. Sketch several papilla? under 

 high power. 





