480 THE SOLIDS. 



semblance ceases, as the thyroid vesicles are most satisfac- 

 torily distinguished from fat globules by their larger size, 

 the fibrous texture of their parieties, and the nature of their 

 contents. 



Such is the general character and appearance of a portion 

 of thyroid examined microscopically ; the entire gland, how- 

 ever, consists of two lobes, which are placed one on each side 

 of the trachea, and which are connected with each other by a 

 narrow slip or isthmus of the gland, and these lobes are 

 further divisible into numerous lobules, many hundreds to 

 each lobe. Now it is these lobules which, so far as the 

 descriptions hitherto given of this gland are to be under- 

 stood, have been regarded and described as the mem- 

 branous cavities of the thyroid (see Plate LXI. fig. 1.), 

 the true and ultimate cellular structure being in general 

 overlooked. 



Thus the lobules are further divisible, each into many small 

 cavities, the ultimate divisions of which the gland is suscep- 

 tible. (See Plate LXI. figs. 2, 3, 4, 5.) These in the slightly 

 enlarged gland are circular, and comparable to fat vesicles 

 (see Plate LXI. figs. 2, 3.) ; but in the gland in its normal 

 state, they are compressed and angular, being also very liable 

 to be altogether overlooked, their size and form being indicated 

 only by certain light-coloured spaces traversing the lobule. 

 (See Plate LXI. fig. 6.) 



Over the surface of each lobule, the blood-vessels form a 

 plexus, from which branches proceed inwards, encircling the 

 vesicles much in the same way as the blood-vessels do the 

 fat corpuscles. (See Plate LXI.jft/. 1.) 



The cavity of each vesicle is perfectly distinct, and does 

 not communicate with that of any other of the vesicles by 

 which it is surrounded : the fibrous tissue, however, of which 

 its walls are so evidently composed (see Plate LXI. fig. 4.) 

 does communicate with and run into that of the neighbouring 

 vesicles, at certain points, however, only. These fibres may 

 frequently be traced from the wall of one cell into that of 

 another ; and it is this fibrous union of the vesicles which 

 renders it impossible completely to isolate any one of the 



