44 THE ESSENTIALS OF HISTOLOGY. 



Lymphoid or adenoid tissue is retiform tissue in which the meshes 

 of the network are largely occupied by lymph-corpuscles. This is by 

 far the most common condition of a retiform tissue, and is met with in 

 the lymphatic glands and allied structures (see Lesson XXII. ), and also 

 in the tissue of the alimentary mucous membrane, and in some other 

 situations. 



Basement membranes (membranse proprise) are homogeneous-looking 

 membranes, which are found forming the surface-layers of connective- 

 tissue expansions in many parts, especially where there is a covering of 

 epithelium, as on mucous membranes, in secreting glands, and else- 

 where. They are generally formed of flattened connective-tissue cells 

 joined together to form a membrane; but, in some cases, they are 

 evidently formed not of cells, but of condensed ground-substance, and 

 in others they are of an elastic nature. 



Jelly-like connective tissue, although occurring largely in the 

 embryo, is found only in one situation in the adult viz., forming the 

 vitreous humour of the eye. It seems to be composed entirely of soft 

 ground-substance, with cells scattered here and there through it, and 

 with very few fibres, or none at all. These several varieties of con- 

 nective tissue will be more fully described in connection with the 

 organs where they occur. 



