39 6 



STRUCTURE OF THE THYMUS. 



[sect. 181. 



Fig. 164. 



ft -^s'Ta 



^Q 



stalk, in the interior of which is a canal. This duct runs through 

 the middle of the gland, and usually presents an irregularly spiral 



arrangement ; its diameter is £'" to i^'". On 

 opening the canal, we find upon its inner sur- 

 face a great number of oblong or fissure-shaped 

 openings, each of which leads into a lobule, 

 and constitutes the outlet of a cavity in the 

 latter. This f thymus-canal/ with the lobules 

 opening into it, presents an obvious resemblance 

 to the excretory duct and the lobules of a true 

 gland; and the similarity is increased by the 

 circumstance, that the lobules consist of smaller 

 subdivisions, which are likewise hollow, aud 

 then, again, of roundish bodies (£■'" to \'") , the 

 gland-granules (or acini of authors), which are 

 the analogues of gland- vesicles of true glands. 

 These elements may be recognised externally 

 upon the lobules, and, by their polygonal form, 

 they give to the surface a beautiful mosaic- 

 work appearance, resembling that of the lungs. 

 These gland- granules, however, are solid bodies, 

 and are not vesicular, like the air-cells of the 

 lungs, although, otherwise, their affinities are 

 with these rather than with any other true 

 glandular element. These gland-granules are 

 intimately united together immediately around 

 the cavity of the lobule, but on its surface they 

 are separated from each other. Thus each 

 lobule may be considered as a thick-walled 

 vesicle furnished with dilatations, the inner 

 surface of which is even and undivided, whilst 

 the outer is separated by fissures, more or 

 less deep, into the above-mentioned gland-granules. 



In many cases, a deviation from the conditions just described is 

 met with, when the thymus, instead of a narrow canal, into which 

 the cavities of the lobules open, contains an actual elongated 

 cavity, \'" to i" in breadth, with which the lobules communicate 

 by large fissure- shaped openings. Many anatomists, and, among 

 the modern, A. Cooper especially, regard the presence of the cavity 

 as normal ; whilst others, with Simon at their head, are inclined 

 to view it as produced by the manner in which the gland is exa- 

 mined (injection, or blowing-in of air). For my own part, I must 



A piece of the thymus 

 of the calf, spread out. 

 a. Chief canal. 6. Lo- 

 bules, c. Isolated gland- 

 granules, seated upon 

 the principal canal. Na- 

 tural size. 



