SECRETION. 



larger in the foetus, and in early life, than in the adult ; but 

 Sappey, from his own researches, is disposed to believe that 

 its weight, in proportion to the weight of the adjacent organs, 

 does not vary with age. 1 It is a little larger and more promi- 

 nent in the female than in the male. 



Structure of the Thyroid Gland. The gland is covered 

 with a thin but resisting coat of ordinary fibrous tissue, which 

 is loosely connected with the surrounding parts. From the 

 internal surface of this membrane are numerous fibrous bands, 

 or trabeculae, giving off, as they pass through the gland, sec- 

 ondary trabeculse, and then subdividing, until they become 

 microscopic. By this arrangement, the gland is divided up 

 into communicating cells, like a sponge. These bands are 

 mingled with numerous small elastic fibres. Throughout 

 the substance of the gland, lodged in the meshes of the tra- 

 beculae, are numerous rounded or ovoid closed vesicles, meas- 

 uring from ^-J-g- to -g-J-g- of an inch. These are formed of 

 a structureless membrane, and lined by a single layer of pale, 

 granular, nucleated cells, from 3^0 to g^ of an inch in 

 diameter. 3 The layer of cells sometimes lines the vesicle 

 completely, sometimes it is incomplete, and sometimes it is 

 wanting. The contents of the vesicles are a clear, yellowish, 

 slightly viscid, albuminoid fluid, with a few granules, pale 

 cells, and nuclei. Robin has described in these vesicles some 

 curiously-shaped, translucent, feebly-refracting, colorless 

 bodies which he lias called sympexions ; but little is known 

 of their constitution or properties. 3 The vesicles are arranged 

 in little collections or lobes, with the great veins passing be- 

 tween them. 



Vessels and Nerves. The blood-vessels of the thyroid 

 gland are very numerous, it being supplied by the superior 



1 SAPPEY, Traite d'anatomie descriptive, Paris, 1857, tome iii., p. 447. 



2 KOLLIKER, Handbuch der Gewebelehre des Menschen, Leipzig, 1867, S. 481. 



8 LITTRE ET ROBIN, Dictionnaire de medecine, Paris, 1855, Articles, Sym- 

 pexion and Thyrco'ide. 



