374 MANUAL OF HISTOLOGY. 



Its gross structure varies in different animals. In some the 

 organ is entirely absent. Its simplest form is found in the rab- 

 bit, where it resembles a large lingual f ollicular gland. In man 

 its usual shape is ovoid. Its average vertical diameter is 20 

 mm., and its transverse diameter 13 mm. Its surface is per- 

 forated by a varying number of slit-like and circular depres- 

 sions, the common orifices of the system of cavities which it 

 contains. If the tonsil of the rabbit be considered a single 

 follicular gland, we have in man a multiplication of this to the 

 number of from eight to eighteen, the interval between each 

 gland forming a " lacuna tonsillaris," crypt, or one of the sys- 

 tem of cavities mentioned above. There are also in the interior 

 of the tonsil single larger cavities, each of which includes sev- 

 eral follicular folds and procures their common discharge at 

 the periphery. The crypts generally are filled, more or less, 

 with a yellowish substance composed of fat-molecules, detached 

 pavement-epithelium, lymph-corpuscles, small molecular gran- 

 ules, and cholesterin- crystals, which probably proceed from 

 retained and decomposed epithelial matter, and perhaps now 

 and then from the bursting of follicles whose cells have in- 

 creased by proliferation and have undergone retrograde meta- 

 morphosis and fatty degeneration. In its minute anatomy the 

 tonsil is for the most part like other so-called adenoid glands. 

 In common with the rest of the oral cavity, it is invested with 

 a thick covering of pavement-epithelium, which rests upon a 

 delicate endothelioid basement-membrane. Following this is a 

 tolerably compact mucosa, formed of interlacing bands of 

 fibrous connective tissue and containing many connective-tis- 

 sue corpuscles. In the normal adult tonsil this structure is so 

 delicate that sometimes it is hardly recognizable. From it 

 bands of connective tissue extend centrally into the larger ton- 

 sillary folds, and the whole forms essentially both an enclosure 

 and a framework for the adenoid tissue or proper substance of 

 the gland, as well as a nidus for its vessels. The minute struc- 

 ture of the adenoid tissue of the tonsil does not differ from 

 that of other follicular glands (those of the intestine, etc.), de- 

 scribed elsewhere. Occasionally, in the tonsil the adenoid tis- 

 sue extends so near the periphery as to penetrate the mucosa 

 and encroach upon the epithelial layers. This is especially 

 the case in the walls of the crypts, where the epithelium com- 

 monly exists in a modified form, or is altogether wanting. The 



