566 THE DUCTLESS GLANDS ENDOCEIN GLANDS 



studies of Hammar (1906) and others indicate that the thymus nor- 

 mally continues its development until about the time of puberty. 

 Subsequently it loses slowly in weight, but a true atrophy of the 

 parenchyma with cessation of function, does apparently not occur until 

 about the age of fifty. 



It is still uncertain whether the thymus should be classified with 



FIG. 487. A SECTION THROUGH SEVERAL LOBULES OF THE THYMUS OF AN INFANT. 



a, loose fibrous septum between the lobules; b, cortex, and c, medulla of the lobule; 

 d, blood-vessels in the connective tissue. Hematein and eosin. Photo. X 60. 



lymphoid organs or with endocrin glands. Recent investigations in- 

 creasingly indicate that it is essentially of lymphoid character but func- 

 tions, in part at least, as an organ of internal secretion, related to 

 normal growth and sexual development. 



At its maximum the thymus forms a large lymphoid mass, embedded 

 in areolar connective tissue, the trabeculas of which divide the organ 

 into several lobes and innumerable minute lobules. Each lobule is 

 surrounded by a thin fibrous capsule, by which it is loosely united to its 

 neighbors. 



The lobule consists of a mass of lymphoid tissue, which is dense at 

 the periphery but looser in the central portion. It is thus divisible 

 into a dense cortex and a loose medulla, both composed essentially of 

 lymphoid tissue, but between which, because of the difference in density, 

 there is a sharp line of demarcation. Frequently, at some point on 



