THE THYROID GLAND. 



587 



Fig. 241. 



body and its vesicles, termed colloid, cannot be doubted, although this 

 morbid condition is so frequent, in certain minor degrees, that many 

 authors enumerate it under the physiological occurrences. In this de- 

 generation, there is deposited in the gland vesicles, which increase in 

 size at the same time, the 

 colloid substance, which also 

 occurs in other situations, in 

 the form of transparent, amor- 

 phous, light yellowish, soft, 

 solid, masses, by which they 

 are more or less filled. In the 

 lesser degrees of this change, 

 the vesicles are but little en- 

 larged, to as much as 0-05 of 

 a line in a transverse section, 

 presenting the appearance 

 of transparent yellowish-white 

 spots or granules, which have 

 been very aptly compared, by Ecker, with boiled sago, and otherwise 

 retaining the usual structure. In a higher degree, the vesicles contain- 

 ing colloid are transformed into larger cysts, of yo-J of a ^ ne ? i n which 

 the epithelium is rarely any longer distinct, but, together with the ab- 

 normal contents, rounded, pale cells, filled with colloid matter or gra- 

 nules, and nuclei, may occur ; these cysts compress the stroma and 

 ultimately, owing to a partial absorption of the walls, coalesce into still 

 larger sinuous cavities, the contents of which are afterwards frequently 

 altered in various ways, by extravasations and their metamorphoses. 

 In Mammalia and Birds, the thyroid body also occasionally contains 

 gland-vesicles slightly distended with colloid matter. 



The bloodvessels of the thyroid gland are, as is well known, dispro- 

 portionately numerous, but in their coarser ramifications present nothing 

 worthy of remark. Each gland-vesicle is provided with some smaller 

 arteries, the subordinate branches of which are distributed and sub- 

 divided in the stroma between the vesicles, finally constituting around 

 each of them a delicate capillary plexus, with rounded-angular and 

 elongated meshes of 0-008-0-016 of a line, and vessels of 0-003-0-005 

 of a line, resembling that of the air-cells, except that the interstices are 

 wider. From this plexus the veins arise, which, in their further course, 

 only partially accompany the arteries, which they much exceed in 

 number. Lymphatics also occur in considerable number in the thyroid 

 gland; the relations of which, however, in the interior, are unknown. 

 The few nerves, lastly, are only vascular nerves, and are derived from 

 the cervical portions of the sympathetic. 



FIG. 241. Gland-vesicles of the thyroid gland, filled with colloid matter, magnified 50 

 diameters. 



