180 THE ORGANS 



and connective tissue, until by the twentieth year scarcely a vestige 

 of glandular tissue remains. The fully developed thymus presents 

 the following structure. The entire gland is surrounded by a rather 

 delicate and loose connective-tissue capsule which attaches it to the 

 surrounding tissues. From the capsule septa extend down into the 

 organ. These branch and subdivide the gland into lobes and lobules. 

 From the perilobular connective tissue, septa extend into the lobule, 

 incompletely separating it into a number of chambers. Each lobule 

 consists of a cortical portion and a medullary portion. The cortex 



Fig. 105. — From Section of Human Thymus, showing parts of five lobules and 

 interlobular septa. X20. (Technic, page 182.) a, Cortex; b, medulla; c, interlobular 

 septum. 



consists of nodules of compact lymphatic tissue, composed of reticular 

 tissue and lymphoid cells, similar to those found in the lymph node. 

 These occupy the chambers formed by the connective-tissue septa. 

 The medulla consists of the same elements only more loosely arranged, 

 the cells being much less closely packed, thus forming a more diffuse 

 lymphatic tissue. There are also in the medulla no connective-tissue 

 septa. In some lobules the more dense cortical substance completely 

 encloses the medulla. It is common, however, for the medullary 

 tissue to extend to the surface of a lobule at one or more points and 

 to be there continuous with the medullary substance of an adjacent 

 lobule. These interlobular connecting strands of medullary substance 



