294 



HISTOLOGY 



invagination of the wall of the oesophagus. 

 These first diverticula are lined with colum- 

 nar epithelium differing but little from the 

 epithelium of the oesophagus. These sacs are 

 mere storehouses for the products of the 

 true glands. The second and third pair of 

 diverticula are but pairs of swollen regions 

 in a single pair of glands. Each gland ex- 

 tends from the fourteenth segment anteri- 

 orly to the tenth, where it opens into one of 

 the first pair of diverticula. Such a gland 

 consists of a number of flattened tubes with 

 relatively wide lumina. These tubes lie 

 longitudinally between the epithelium of the 

 oesophagus and the layer of circular mus- 

 cles. The glandular tubes have in trans- 

 verse section the outline of truncated wedges ; 

 these flattened glands lie with their flattened 

 sides radiating from the oesophagus. They 

 are of mesenchymal origin. Each tube is 

 coated with a membrana propria or base- 

 ment membrane. The wall of the tube is 

 formed by a deep syncytial layer. The cyto- 

 plasm of this syncytium is alveolar in its 



FIG. 258. Details of last figure _,, . .. . 



at x enlarged, en.c., enamel appearance. The inner margin of the cyto- 



cells; en.l., enamel layer; d.c., plasm Varies with the functional periods. 

 dentine cells ; d.l.. dentine layer. T ., . ., , . , . -, . , ,. . . 



x 700 Likewise the nuclei, which arise by division 



near the membrana propria, vary in size, 



shape, and position. The nuclei when young are oval and lie near 

 the membrana propria, with their long axes 

 parallel to the base of the syncytium. In the 

 height of their development the nuclei are 

 spherical and lie near the middle or towards 

 the margin of the cytoplasm. The secretion of 

 lime takes place near the margin of the cyto- 

 plasm. In the elaboration of lime or calcium 

 carbonate both the marginal nuclei and the 

 cytoplasm disintegrate (Fig. 259). 



Mucous glands from the base of the tongue 

 of a bat will serve to show an accessory ali- FlG 2S9 ._ section *of a por- 

 mentary tissue used for lubrication. Each of tion of epithelium from the 

 these glands is a branching tubular gland. Its J 

 cells are tall columnar elements measuring (After HARRINGTON.) 





