SECT. 1 8 1.] THE THYMUS. 395 



describes a hypertrophy of the thyroid by multiplication of the normal 

 elements of the gland, new vesicles arising partly independently, partly by 

 internal growth from the walls of enlarged vesicles. 



According to Remak, the thyroid body is developed by the separation of a 

 part of the anterior wall by the gullet, and division of this into two halves. 

 In a human embryo at the third month, I found the thyroid already composed 

 of isolated vesicles, o'oi6"' to 0-05'" in diameter, which consisted of a homo- 

 geneous envelope, including roundish or angular cells. I think that I have 

 ; th< se follicles multiply by sending out roundish processes, which after- 

 wards separate. If this be really the case, the whole process of formation of 

 the thyroid may, perhaps, be regarded as a continued growth and division of 

 the follicles ; the division of its primitive vascular rudiment, as observed by 

 11 ruak, 1 icing only the first phase of it. In this way, a certain resemblance 

 to the thymus would also be established, only that in the thymus the two 

 first rudimentary processes, as well as subsequent ones, become severed from 

 each other, and only retain a slight connection. According to the above 

 v, the follicles of the thyroid are not enlarged cells, still less are they 

 metamorphosed nuclei {Rokitansly), but they have the value of true gland- 

 follicles. 



In the investigation of the vesicles of the thyroid, the organ shoidd be 

 examined in children, and in the lower animals, in birds and amphibia espe- 

 cially. Sections made with the double knife are best adapted for the study 

 of the disposition of the vessels, and of their relation to each other ; but this 

 object may also be attained by carefully teasing out the parts under the 

 microscope. The vessels may be very easily and completely injected in 

 children. The network of capillaries around the vesicles is best seen in 

 sections near the surface. 



Literature. — Schwager-Bardeleben, Obs. Micr. de Glandularum Duetu 

 E ■ret. Carentium Struct., Berol., 1841, Diss. Panagiotides, De Glandul. 

 Thyreoidece Structura Penitiori, Diss. Berol., 1847. The same author with K. 

 Wagener, Some Observations on the Thyroid Gland, in Fror. A r . JS T ot., vol.xl. 

 p. 193. A. Ecker, in Hexle and Pfeuffer's Zeitschrift f. rat. Med., vi. bd., 

 p. 123 ; and Article BlutgefassdrUsen, in Wagner's Handw. d. Physiol., iii. 

 ROKTPANSKY, in Zeitschrift d. Wiener Aertze, 1847 ; and On the Anatomy of 

 Goitre, in Denkschriften der Eaiserl. Ahead, m Wien, bd. i., Wien, 1849. E. R. 

 le Genpre, Be la Thyroide, these, Paris, 1852. Kohlrausch, in Mull., Arch. 

 1853, p. 142. 



Of the Thymus. 



§ 181. The thymus is another of the so-called ' vascular glands.' 

 It is a double, elongated organ, flattened and broader inferiorly, and 

 is enveloped and connected with neighbouring parts by loose con- 

 nective tissue. Even on superficial examination, we may see larger 

 lobules, averaging from 2'" to 5'" in size, and having a roundish, 

 oblong, or pyriform shape, mostly compressed against each other. 

 These lobes are only connected by yielding connective tissue, and can 

 be separated without difficulty. Tracing the lobes to their inner 

 attachment, they are all found to be attached singly to a common 



