186 SPECIAL HISTOLOGY. 



and is in general, spirally convoluted, though not quite regularly 

 so. When this canal, normally J — li"' in diameter, is opened, 

 there are found on its inner surface a great number of oval 

 fissures or apertures, each of which leads to a lobule and consti- 

 tutes the outlet of a cavity contained in it. The resemblance 

 of this canal of the thymus and of the closely approximated 

 lobules opening into it, to the excretory duct and the lobules of 

 a true gland, is still further heightened by the circumstance, 

 that the lobules are composed of smaller, also hollow subdivi- 

 sions and the latter of rounded corpuscles, | — J"' in size, like 

 gland- vesicles, the gland-granules (acini of authors), which 

 may be recognised even on the exterior and, from their 

 polygonal shape, give the surface of the lobules a delicate 

 mosaic aspect, not unlike that of the lungs. These gland- 

 granules, however, are not vesicles at all, such as the air- 

 cells, which, among the elements of the true glands, ap- 

 proach nearest to them in size, but solid bodies, which, 

 towards the cavity of the lobules or its accessory cavities, are 

 intimately coherent, whilst on the outer side they are separated 

 from each other. Each lobule may also be regarded as a 

 thick-walled vesicle, with protrusions, whose inner surface 

 is even and continuous, whilst the outer is subdivided into the 

 above-mentioned gland-granules, by more or less deep fissures. 

 In many cases, a condition different from that just described 

 is met with, inasmuch as, instead of a contracted canal, into 

 which the cavities of the gland-lobules open, each thymus 

 contains a larger though contracted cavity, \ — 1" wide, with 

 which the gland-lobules communicate by larger fissure-like 

 openings. Many anatomists, and among the more modern, par- 

 ticularly Sir A. Cooper, consider the existence of this cavity 

 as normal ; whilst others, at the head of whom is Simon, are 

 disposed to regard it as produced by the methods of investiga- 

 tion employed (injections, inflation). I believe that Simon is 

 correct, when he asserts that in such a delicate structure as 

 the thymus, injection or inflation, unless effected with the 

 greatest care, necessarily lead to error and I am also satisfied, 

 that many of the observed " reservoirs w in the thymus are only 

 artificially produced ; but, nevertheless, I am of opinion, that 

 there really are thymus glands, containing, in life, a central 

 cavity, because I have seen such cavities extending through the 



