THYMUS 



223 



Hewson it gradually wastes until the child has reached between its tenth 

 and twelfth year, when ordinarily it is perfectly effaced, leaving only liga- 

 mentous remains. These older observations have been generally ac- 

 cepted, and the persistence of the thymus in the adult is regarded as of 



Thymic 

 corpuscles. 



J Connective tissue. 



Transverse section 

 of blood vessel. 



~- Medullary cord. 



Cortex. 



Medulla.- 



Blood vessel. 



Thymic 

 corpuscle. >*, 



FIG. 212. FROM A CROSS SECTION OF THE THYMUS OF A CHILD, ONE YEAR AND NINE MONTHS OLD. X 21. 



considerable pathological importance. According to Waldeyer and Ham- 

 mar, however, it persists for a much longer time. It increases in size 

 and weight for some years after birth, probably until puberty, and then 

 slowly atrophies. At fifteen years it is said to weigh 40-50 grams. It is 

 considered an active organ 

 even to the fortieth year, 

 losing its functions with 

 beginning old age (50-60 

 years). The duration of 

 the thymus has apparently 

 been underestimated. (See 

 Hammar. Arch. f. Anat. u. 

 Entw., 1906, Suppl.-Bd. pp., 

 91-182; Anat. Anz., 1905, 

 vol. 27, pp. 23-89; and for 

 development, Anat. Hefte, 

 Abth. i, 1911, vol. 43, pp. 

 203-242). 



The thymus is subdivi- 

 ded by connective tissue 



layers into lobes from 4 tO FlG - 213. PART OF A SECTION OF THE THYMUS FROM A HUMAN 

 * EMBRYO OF FIVE MONTHS. X 50. 



ii mm. in diameter, and 



these are similarly subdivided into lobules of about i cu. mm. each. All 

 the lobules in the right and left halves of the thymus, respectively, are 

 attached to a cord of medullary substance, 1-3 mm. in diameter, as may 

 be seen if the gland is pulled apart. This axial structure suggests the 



Tangential sections of lobules. 



