OF THE THYMUS GLAND. 261 



observing, that the thymus exists during the early periods of 

 life only, when those particles seem to be most wanted (cxxvn). 

 SECT. 39. Probably the thymus is formed in the human 

 embryo, in the same proportion with all the other parts of the 

 animal. It appears distinctly about the end of the third or 

 beginning of the fourth month from conception. From this 



(cxxvu.) In the calf, Sir Astley Cooper a describes two large vessels, 

 which he declares to be the absorbent ducts of the thymus, running 

 upon its posterior surface, carrying the fluid of the gland, and ter- 

 minating in the jugular veins at their junction with the superior cava 

 by one or more orifices on each side. He dissents from the opinion 

 that the structure of the thymus and of the absorbent glands is similar. 

 " One is conglobate and the other conglomerate ; one is firm and 

 compact, and the other loose and pulpy; the one contains cells of 

 considerable magnitude when in the distended state, whilst in the ab- 

 sorbent glands the cavities are small, and with so much difficulty traced, 

 that there is still a doubt if they be cellular or vascular." The structure 

 of the lymphatic glands is noticed in Sect. 12 and Note cxix*. Sir 

 Astley concludes, like some of the old anatomists, as Glisson b and 

 Dionis, c that the use of the thymus d is to prepare a fluid well fitted for 

 the growth and nourishment of the foetus, before its birth, and con- 

 sequently before chyle is formed from the food. But the thymus is 

 not merely an organ to supply the wants of foetal life ; for, as I have 

 noticed in the Appendix to the English edition of Gerber's ' Anatomy,' 

 pp. 97-8, the functions of the gland are very active some time after 

 birth, at which period Dr. Haugsted 6 has proved, in brutes, that the de- 

 velopment of the thymus, both proportional and absolute, is greatest. 



According to my observations, just cited, the thymus and its juice 

 soon become diminished in ill-fed, over-fatigued, and diseased young 

 brutes, and in badly-nourished and diseased infants. On this subject 

 my friend Dr. Boyd, who has long been employed at the parochial 

 infirmary of St. Marylebone, in researches concerning the weight of the 

 human organs, has given me- the following note : 



" The weight of the thymus, in 170 cases, was found to vary more 

 than any other organ, in early life. In a female foetus, 10 inches long 

 and 10i ounces weight, the thymus weighed 6 grains; in a still-born 

 female, 22 inches long and 9 Ib. 10 oz. weight, the thymus weighed 

 340 grains. In 7 male still-born children, out of 24 examined, the 

 thymus weighed half an ounce and upwards, and its average weight 

 was 154 grains. In 3 female still-born children, out of 25 examined, 

 the thymus also weighed half an ounce and upwards, and its average 

 weight was 148 grains. 



"The weight of the thymus was greater in males than in females; 



a Anatomy of the Thymus Gland, pp. 14, c Anatomic de 1'Homme, 5th ed. p. 497, 

 15, 38, 44, 8vo, Lond. 1832. 8vo, Paris, 1716. 



b Anatomia Hepatis, cap. xlv, p. 443, d See Note CXLIV. 



8vo, Lond. 1654. e Thymi Descriptio Anatomica, cap. xi, 



pp. 89 et seq., 8vo, Hafniae, 1832. 



