182 



SPECIAL HISTOLOGY. 



Fig. 241. 



the vesicles are but little enlarged, to as much as 0*05 , 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 trans- 

 formed into larger 

 cysts, of i— i\ . in 

 which the epithelium 

 is rarely any longer 

 distinct, but, together with the abnormal contents, rounded, 

 pale cells, filled with colloid matter or granules, 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 blood-vessels of the thyroid gland are, as is well known, 

 disproportionately 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 be- 

 tween the vesicles, finally constituting around each of them a 

 delicate capillary plexus, with rounded-angular and elongated 

 meshes of 0-008 — 0-016'", and vessels of 0'003— 0-005"', re- 

 sembling 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, 



Fig. 241. Gland. vesicles of the thyroid gland, filled with colloid matter, x 50 

 diam. 



