STKUCTURE OF THE THYMUS GLAND. 367 



which, as may be particularly well seen in the thymus of the dog, 

 is usually composed of fine fibres, arranged in the form of delicate 

 rhombic meshes. These are generally filled with more or less 

 closely packed large cells; but near the free surface of the folli 

 cles, where they are not confluent with one another, the cells 

 are smaller and more crowded, whilst the tissue becomes so con- 

 densed as to form a kind of capsule. The individual follicles are 

 either entirely thus encapsuled and isolated, as frequently occurs 

 in the calf, or several may be united at their centric portion, as 

 in the dog and man. On the whole, their structural characters 

 are comparable with those of the Peyer's patches of the small 

 intestine. 



The form of the several follicles is elongated, spheroidal, or 

 polyhedral, and those situated near the surface are always 

 larger than those more deeply seated ; those of the dog and calf 

 are usually elliptical in form. 



The finer structure of the follicles displays the same mor- 

 phological elements, with the same relative disposition, as the 

 ordinary lymph follicles. According to His,* fine capillary 

 bloodvessels, proceeding from the vessels running in the septa, 

 penetrate the follicles at numerous points of their surface, 

 and in consequence of these frequent anastomoses, form a 

 very close-meshed plexus. Between the vessels, and attached 

 to them, as well as to the connective tissue of the septa, an 

 exceedingly compact, but very delicate, network is extended, 

 chiefly formed by the anastomosing branches of multipolar 

 cells, in the interstices of which are numerous lymph cells ; 

 in addition a narrow-meshed network may be distinguished, 

 resembling the above, except in the absence of cells, and in 

 the greater breadth of the trabeculae, especially at their 

 nodal points. These narrow-meshed networks are the pro- 

 longations of the interalveolar or interfollicular lymphatic 

 vessels. Lastly, there occurs a third kind of trabecular 

 structure in the form of strong elongated fibres, which 

 are stretched between adjoining vessels, or between these 



* Beitrdge zur Kenntniss der zum Lymphsysteme gehorigen Driisen, 

 Siebold and Kolliker's Zeitschrift filr wissenschaftliche Zoologie, Band x., 

 p. 333. 



