368 THE THYMUS GLAND, BY E. KLEIN. 



and the septa of connective tissue. These are not much 

 branched, and are attached by means of conical longitudi- 

 nally striated bases to the vessels. 



The contents of the follicles, that is to say, of the trabecular 

 structures, consist of cells, which, according to their size, may 

 be arranged in three categories. Of these the first, and by 

 far the most numerous, are ordinary lymph corpuscles ; the 

 second are larger coarsely granular spheroidal bodies, composed 

 of protoplasm, and containing one or several nuclei ; and the 

 third are Hassall's concentric corpuscles, of which Ecker * re- 

 cognises two forms, one simple and the other compound. The 

 former are spheroidal vesicles, varying from 0'0075 to O009 

 millimeter in diameter, containing in the interior of their con- 

 centrically striated sheath sometimes only a homogeneous mass 

 with fatty lustre, but sometimes a nucleus and granular material. 

 These last are as much as O027 millimeter in diameter, and are 

 composed of several simple vesicles that are collectively invested 

 and united together by a concentrically striated membrane. 

 Both species of the concentric bodies occur, according to Ecker, 

 at every stage of development ; yet with increasing abundance 

 as the gland gradually advances to complete maturity. 



VESSELS. In the calf and in man the larger branches run- 

 ning in the follicular septa divide into numerous branches 

 that everywhere surround the follicles, f The arteries give off 

 capillaries that penetrate into their interior, and after communi- 

 cating by transverse branches, run in a radial direction, and 

 terminate in circular vessels. As a rule the latter do not quite 

 reach the centre of the follicles, but become continuous with 

 veins which accompany the arteries. 



The distribution of the vessels in the thymus of the dog pre- 

 sents some difference from that which has just been described. 

 Here the larger trunks situated in the septa give off branches 

 that penetrate into the interior of the follicles, and then break 

 up at the outer part into a capillary network, by which they 



* Blutgefassdrusen in R. Wagner's Ilandworterbuch, Band i., p. 115. 

 t Ecker, loc. cit., and His, loc. cit. 



