TONGUE. 6 1 



fibres disposed vertically, and terminating above in tendons continuous with the connective 

 tissue of the mucous membrane. Immediately under the mucous membrane of the dorsum 

 notice the transverse sections of longitudinal muscular fibres. Between the muscular fibres many 

 fat-cells are seen, and excellent sections of nerves, and the branches of the ranine artery are 

 found in the lower part. {Indicate the general arrangement of the parts in one half off\. XII., 

 Fig. i.) (H). Study the papillae, and the epithelium covering them. The upper layers of 

 the epithelium are often horny, especially in animals. Notice the transverse sections of 

 muscular fibres polygonal in shape with the nuclei placed just under the sarcolemma (PI. 

 XII., Fig. 2). 



POSTERIOR PART OF THE TONGITE. Prepare this just as the anterior part, and 

 make vertical sections. Here the mucous membrane is much thicker and looser, and contains 

 many secreting glands, lymphatic follicles, and diffuse adenoid tissue. Stain a section with 

 logwood and mount it in dammar. 



EXAMINATION (L). Perhaps the section may have passed through a circumvalate 

 papilla. Study specially the secreting- glands, which are of two kinds, mucous and serous 

 (v. Ebner). The mucous (L and H) glands are like similar glands in the mouth and oesopha- 

 gus (p. 65). Each gland consists of a duct and a secreting part. The duct passes vertically 

 and opens on the free surface, often with a funnel-shaped mouth. It has a wide lumen, and a 

 membrana propria with oval nuclei, lined by a layer of columnar epithelium. The duct 

 branches and terminates in the secretory part, which consists of more or less convoluted tubes, 

 so that each gland is a compound tubular gland. The cells lining the secretory alveoli consist 

 of a single layer of low columnar epithelium, and their appearance is very characteristic, 

 especially when they are distended. They are clear and transparent, with a thin oval nucleus 

 pushed to one side. They contain a delicate network of fibrils distended with ' mucigen,' 

 which yields mucin. During a state of exhaustion these cells are more ' granular.' The 

 serous glands (L and H) always bear a relation to the taste-bulbs, and these ducts open into 

 grooves which contain these bulbs. The secreting epithelium is columnar with a spherical 

 nucleus, and the protoplasm is very granular, due to the existence of a dense fibrillar network. 

 This markedly granular character at once distinguishes them from the clear transparent cells 

 of the mucous glands. They seem to secrete a watery fluid. In the same section patches of 

 adenoid tissue may be found. 



Double-Staining of the Tongue with Logwood and Iodine Green. Stain a vertical section of 

 the posterior part of the tongue lightly in logwood, wash it thoroughly, and then stain it 

 slightly in a weak watery solution of iodine green (p. xlv) ; mount in dammar. The striking 

 feature is that the acini of the mucous glands are stained of a bright green, while the 

 epithelium in the efferent duct is of a logwood tint. A high power reveals the nuclei stained 

 with logwood. The serous glands do not take on any of the green pigment, so that the two 

 kinds of glands stand out in striking contrast. Make a similar preparation with picrocarmine 

 and iodine green as indicated for the small intestine (p. 69) ; mount in dammar. All the muscle 

 will be yellowish-red, the connective tissue deep red, and the adenoid tissue and mucous glands 

 bright green. 



Blood-vessels of the Tongue. Mount a vertical section of an injected tongue in dammar. The 

 blood-vessels present nothing peculiar. Trace branches into the papillae. If the papilla be simple 

 it contains a single capillary loop ; if compound, each secondary papilla contains a similar loop. 

 (Fill in the blood-vessels in one half of PL XII., Fig. i.) 



Nerves of the Tongue. Many sections of the hypoglossal nerve will be found near the 



