328 THE DUCTLESS GLANDS. [CH. xxm. 



cell stations in the sympathetic chain (Schafer) or semi-lunar 

 ganglia (Langley). 



The preceding figure (fig. 300) shows a typical tracing 

 obtained by Schafer's instrument, from a dog's spleen. 



The Thymus. 



This gland is a temporary organ ; it attains its greatest size 

 early after birth, and after the second year gradually diminishes, 

 until in adult life hardly a vestige remains. At its greatest develop- 

 ment it is a long narrow body, situated in the front of the chest 



Fig. 301. Transverse section of a lobule of an injected infantile thymus gland, a, capsule 

 of connective-tissue surrounding the lobule ; b, membrane of the glandular vesicles ; 

 c, cavity of the lobule, from which the larger blood-vessels are seen to extend 

 towards and ramify in the spheroidal masses of the lobule, x 30. (Kolliker.) 



behind the sternum and partly in the lower part of the neck. It 

 is of a reddish or greyish colour, and is distinctly tabulated. 



Structure. The gland is surrounded by a fibrous capsule, which 

 sends in processes, forming trabeculse, that divide the gland 

 into lobes, and carry the blood- and lymph-vessels. The large 

 trabeculse branch into small ones, which divide the lobes into 

 lobules. The lobules are further subdivided into follicles by fine 

 connective-tissue. A follicle (fig. 303), is seen on section to be 

 more or less polyhedral in shape, and consists of cortical and 

 medullary portions, both of which are composed of adenoid or 

 tymphoid tissue, but in the medullary portion the matrix is coarser, 

 and is not so filled up with lymphoid corpuscles as in the cortex. 



