MR. E. C. BABER OR THE STRUCTURE OF THE THYROID GLAND. 
579 
appeared to be a broad band of small lymphatics became injected, running across the 
trachea to the lower part of the opposite lobe. Sections of this connecting band, 
examined microscopically, showed that it contained a considerable quantity of gland- 
tissue, and was therefore a true isthmus. In the Kitten, on injecting one gland 
by the puncture method with Berlin blue solution, what was apparently a large 
lymphatic vessel became filled, running across the trachea to the lower part of the 
opposite gland. This probably also formed a delicate isthmus of gland-tissue, connect¬ 
ing the two lobes. 
Aves .—In the Birds examined (Fowl, Book, Pigeon) the thyroid gland was composed 
of two small round or elongated bodies, situate in the upper part of the thorax, and in 
close connection with the jugular vein and carotid artery on either side. 
Re pt ilia .—In the Tortoise the gland is single, and forms a yellowish, rounded, 
somewhat flattened organ, situate just above the base of the heart, between the right 
and left aorta. 
Amphibia. — Frog. The following extracts will show that observers are by no 
means unanimous in regard to the position and character of the thyroid gland in this 
animal. 
Leydig {op. cit., p. 376) says that the thyroid gland of tail-less Batrachians (Frogs 
and Toads) usually consists of only three large vesicles, provided with a fine capillary 
network and isolated from one another, whose contents are neither clear fluid nor 
colloid, but a finely granular and partly fatty substance. Bolleston {op. cit., 
pp. 184, 185) describes and figures the thyroid glands as placed just internally to the 
jugular veins. Huxley and Martin {op. cit., p. 181), on the contrary, state that 
“ the thyroid gland appears to be represented by two or more oval bodies, which are 
found attached to the lingual vessels, and between the aortic and pulmo-cutaneous 
trunks.” W. Muller {op. cit., p. 438) found that in young Frogs the thyroid lay on 
the two sides of the body of the hyoid bone, close in front of the point of attachment 
of the cornua tliyreoidea. It was surrounded on all sides by muscles, and possessed a 
thin connective-tissue capsule, from which the vessels with their connective-tissue 
adventitia stretched into the interior. The gland substance consisted entirely of closed 
vesicles, with a delicate membrana propria and a single layer of cubical epithelium 
without pigment, and a central cavity containing a transparent colourless fluid, without 
any structural elements. 
For some time I was unable to find in the Frog any body corresponding histolo¬ 
gically to the thyroid gland, but subsequently, by following W. Muller’s directions 
as just quoted, I discovered it in transverse sections of the head. My observations 
show that in the Frog there are two bodies presenting the structure of the thyroid 
gland. They are situate, one on either side, on the ventral surface of the hyoid 
cartilage (or bone), being usually, but not always, in direct contact with this struc¬ 
ture. They are found either between the hyoid cartilage and the hyoglossus muscles, 
or else immediately to the outer side of these muscles, on a level just anterior to the 
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