592 SPECIAL HISTOLOGY. 



apparent that other elements, to some extent of quite an unexpected 

 kind, enter into its composition ; as for instance, bloodvessels, and also 

 a smaller quantity of a, fibrous substance of the nature of connective tis- 

 sue, so that a structure not unlike that of the contents of the Peyerian 

 follicles is presented. 



Of the elements of the walls of the thymus-lohules, the vesicular, 

 together with a small quantity of a connecting fluid, constitute the main 

 bulk. Among these, free nuclei 0*002-0*005 of a line in size, of a 

 round slightly flattened shape, with homogeneous, clear contents, which 

 become troubled and granular in soda and acetic acid and with or with- 

 out a nucleolus, are always present in very great numbers. Secondly, 

 as I find, agreeing with Ecker but in opposition to Simon, cells also are 

 never wanting, though existing of very various sizes, from 0*004 to 0*01 

 of a line, and, though varying in number as well, still much less nu- 

 merous than the nuclei. Their nuclei are for the most part simple and 

 distinct, and the contents pale or with scattered fat-granules, or, and 

 this Ecker says that he has noticed after the complete development of 

 the organ, they are without nuclei and entirely filled with fat. In the 

 midst of these elements run numerous bloodvessels of larger and smaller 

 size. The main trunks running on the outer aspect and close upon the 

 central cavity in the longitudinal direction of the organ, give off a large 

 number of branches to the central cavity, which, penetrating its walls, 

 reach its internal surface, and there ramify minutely in a delicate pelli- 

 cle, composed of connective tissue, with which it is lined, anastomosing 

 and also forming tolerably close capillary plexuses. From these arterial 

 plexuses, at every point where the lobules open, numerous vessels arise 

 and enter them, taking their course in the innermost portion of the 

 thick boundary wall, and then ramify towards the exterior in the sepa- 

 rate gland-granules, so as to constitute a capillary plexus entirely filling 

 them, composed of vessels 0*003-0-005 of a line in diameter, and with 

 meshes of 0*01-0*02 of a line (Fig. 244). The distribution of these 

 vessels, in Man, is so limited to the interior of the gland-granules, that, 

 even when these have been most completely displayed, not a single vessel 

 is found on the outer aspect of their structureless investing membrane ; 

 on the contrary they are all seen terminating in loops close upon it. 

 Besides these bloodvessels a small quantity of connective tissue also ap- 

 pears to enter into the formation of the thick walls of the glandular 

 lobes ; at all events, in their innermost portions, where the larger 

 vessels are situated, we find, often with tolerable distinctness, a mem- 

 brane supporting them, analogous to that lining the central cavity. In 

 other cases, however, and especially in animals, an internal limitary 

 membrane of this kind cannot be demonstrated, and the cavities of the 

 lobules are bounded immediately by the granular substance connecting 

 the vessels, between which, only some delicate indications of fibres are 



