GOO 
MR. E. C. BABER OR THE STRUCTURE OF THE THYROID GLAXD. 
blood-corpuscles, are frequently seen in this thyroid gland amongst the vesicles, and 
between these veins and the epithelial wall of the vesicles capillaries often ramify. 
VI. Blood-vessels. 
Literature .—The great richness of the thyroid gland in blood-vessels and the 
abundance of its capillaries, which form extensive ramifications on the surface of the 
vesicles, are generally acknowledged. 
Zeiss {op. ait., p. 34) describes, in specimens in which the blood-vessels are injected 
with Berlin blue, knotty dilatations forming dark blue drops situate laterally on the 
capillaries, or similar structures forming apparently the blind end of a capillary. 
He observed these in the Babbit, Cat, and Bat, and says he was unable to observe 
these peculiar bulging or drop-like dilatations in uninjected specimens, although he 
speaks elsewhere of the capillaries in uninjected specimens being wedged in between 
the epithelial cells, and forming small projections towards the epithelial layer. 
Zeiss considers that the presence in such great numbers of these nodules or dilatations 
on the capillaries may retard to a considerable extent the flow of blood through the 
vessels of the gland, thereby favouring any secretion from, or absorption into, the blood¬ 
vessels, which may take place either in connection with the vesicles or with the 
lymphatics. Neither Boechat nor Beremeschko make any mention of these dilata¬ 
tions, and in the figure which the latter observer gives of the blood-vessels no sign of 
them is visible. 
Observations. —In the thyroid gland of the Tortoise I have frequently observed, in 
transverse sections of the epithelial walls of the vesicles (in uninjected specimens), 
projections of the capillaries between the epithelial cells, towards the interior of the 
vesicles. I have endeavoured repeatedly to show these by injections of the blood¬ 
vessels of the gland in this animal, but without much success, owing to a shrinking of 
the epithelial cells. It appears very probable that it is through these projections of 
the capillaries that the escape of blood-corpuscles (red or colourless) takes place into 
the cavity of the vesicles. In fact, in one specimen I could see in a vesicle, close to 
one of the capillary projections, some red and colourless blood-corpuscles which had 
apparently just escaped from a blood-vessel through this channel. Some peculiarities 
of the blood-vessels in the thyroid glands of Birds have been alluded to under the 
head of lymphatics {vide supra, p. 598), and those of the Conger Eel have also been 
referred to above (p. 599). 
The relation of both large and capillary blood-vessels to the lymphatics has been 
discussed in considering the basement membrane ( vide supra, p. 588). 
VII. Undeveloped portions. 
In the thyroid gland of the Dog bodies of considerable size are frequently seen, 
which differ entirely in structure from the rest of the gland (see Blate 69, fig. 19). 
They are rounded or flattened in shape, usually situate on the surface of the organ, and 
