488 Ralph H. Major. 



rial passes from a follicle into the lymph spaces by a gradual oblit- 

 eration, "melting" or bursting, of some portion of the wall of the 

 follicle. As the meshes in the capillary net are large as compared 

 with the size of the cells, it can be conceived that quite a number 

 of cells can be destroyed without affecting the integrity of the 

 capillary network. Thus an opening sufficient to permit the escape 

 of the colloid material can take place without rupturing a capillary 

 and causing hemorrhage, or at most only a few capillaries need be 

 ruptured. That some capillaries are often ruptured, is shown by 

 the frequent finding of red blood cells in the lymph spaces and in the 

 cavity of the follicle. 



The veins that return the blood from the follicles follow closely 

 the path of the arteries, show frequent anastomoses and finally reach 

 the surface of the gland where they anastomose freely. 



The average size of the arteries of the first order is .15 mm.; 

 those of the second order .1 mm. ; those of the third order .03 mm. ; 

 and lastly the follicular arteries are .0125 mm. in size. The capil- 

 laries of the follicular network average .008 mm. in size. These 

 measurements are those of the normal human thyroid. 



The finer distribution of the blood vessels in the cat's thyroid 

 differs somewhat from that of the dog and man. In the cat the arte- 

 ries of the second order pass between lobes and the arteries of 

 the third order pass between lobules just as in man. Arteries of 

 the fourth order passing to the lobules are also present, but not 

 so constant. In the cat, however, no follicular arteries are present. 

 Each follicle is not surrounded by a rich capillary network and 

 supplied by its own follicular artery, but the follicles are placed in 

 a loose, wide network, each mesh of which in a cross section appears 

 to surround a single follicle. This network has depth as well as 

 lengih and breadth and surrounds the follicle in three dimensions. 

 The arteries which supply the lobules, approach the lobules and 

 immediately split up into capillaries without giving off any follicular 

 arteries. The veins collect from the capillaries at a point somewhat 

 removed from the arteries often directly opposite them, but soon 

 approach them and follow the same general course. 



