262 SITUATION AND STRUCTURE 



period to the time of birth, its size is considerably increased, 

 when it is commonly about the size of a small walnut, though 

 not of that figure. In some it is much bigger, but in others 

 it does not exceed the size of a large filbert-nut. 



SECT. 40. From the time of birth to the end of the first 

 year, the gland continues to grow larger, and keeps pace with 

 the general growth of the other parts of the body. From the 

 end of the first to the third year, it is neither perceptibly in- 

 creased nor diminished, but preserves nearly the same size it 

 had acquired at the end of the first year. From the third to 

 the eighth or tenth, it decreases in size, and, gradually wasting, 

 becomes less and less till the child has reached to between its 

 tenth and twelfth year, when ordinarily it is perfectly effaced, 

 leaving only a ligamentous remains, that degenerates into a 

 kind of reticular substance. As the gland becomes less, the 

 vessels that supplied it with blood for secretion diminish in 

 proportion, and at length when the gland totally disappears, 

 these, like the umbilical vessels, being no longer wanted, de- 

 generate into mere ligaments. Sometimes, though very rarely, 

 they continue pervious, (but their diameters are exceedingly 

 contracted,) and carry blood to the remains of the thymus and 

 the mediastinum. 



SECT. 41. This curious circumstance of the thymus being 

 largest in the earlier periods of life, and becoming gradually 

 less as the animal advances towards maturity, constantly takes 

 place in the human subject, though the periods, when these 



in 86 children, from birth to 2 years of age, who died from various 

 diseases, the average weight of the thymus was 90 grains in 44 males, 

 and 80 grains in 42 females. In 14 males from 2 to 6 years of age, 

 the thymus weighed 104 grains, and 71 grains in 21 females from 2 

 to 18 years of age. 



" In emaciating diseases the thymus wastes rapidly, almost to a mere 

 membrane devoid of juice. In a female aged 13 days, weighing at 

 birth 6 lb., and after death but 3 Ib. 11 oz., the weight of the thymus 

 was only 10 grains; in another emaciated female, aged 18 days, the 

 thymus weighed 15 grains. Of children not emaciated, in one male 

 aged 7 months and in another aged 1 1 months, who both died of acute 

 arachnitis, the thymus in the first was 330 grains, and in the second 

 220 ; and in a female, aged 1 month, who died of convulsions, the 

 thymus weighed 330 grains." 



The size of the lymphatic glands at different periods, is mentioned 

 in Note cxix, page 246. 



