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MR. E. C. BABER OX THE STRUCTURE OF THE THYROID GLAXO. 
In the thyroid gland of the Dog, however, it is remarkable that although these 
bodies are of frequent occurrence, there is, usually, in Dogs aged three months and 
upwards no evidence to show that they are undergoing further development. It is 
an interesting question whether the undeveloped portions, which are distinct from the 
gland, may not under certain circumstances become developed into true gland-tissue, 
and either give* rise to the isolated lobes mentioned by various authors, or simply 
cause an increase in size of the gland itself. 
Masses of lymphoid tissue have been observed in the thyroid glands of Kitten and 
Pigeon. 
GEXERAL COXCLUSIOXS. 
1 . In the Frog, in opposition to the statements of several observers, the thyroid 
gland forms two small bodies situate, one on either side, on the ventral surface of the 
hyoid cartilage (or bone) usually but not always in direct contact with this structure. 
They are placed either between the hyoid cartilage and the hyoglossus muscles, or 
else immediately to the outer side of the latter, just anterior to the point of their 
convergence. 
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2 . In the thyroid gland of adult animals the vesicles form closed cavities which are 
not in communication with one another to any extent. Branched vesicles, which may 
be present in the glands of adult animals, probably merely indicate that an increase in 
the number of vesicles is taking place by the growth into them of involutions of their 
■walls. In the Conger Eel small vesicles are frequently observed in the walls of larger 
ones, into which they appear sometimes to burst by causing a flattening of the 
epithelial walls. 
3. Whilst the shape of the epithelicd cells varies much in different animals, the 
general tendency of these cells throughout the Vertebrate series, as far as examined, is 
to the columnar form. 
A delicate reticulum (as described by Zeiss) is found amongst the epithelial cells of 
the vesicles. In a profile view of the epithelium club-shaped cells are also often seen, 
which are probably more or less branched cells situate in the swollen parts of the 
reticulum. 
The only form of basement membrane observed has been a delicate layer of connective 
tissue between the epithelium and the endothelium of the lymphatics in which the 
blood-vessels ramify. 
4. The following are the chief contents of the vesicles which have been observed in 
the microscopical examination of specimens hardened in alcohol. 
(a) Homogeneous or granular material (“colloid substance ” of authors) has been 
observed with slight variations in all classes of the Vertebrata, and is undoubtedly 
a normal product of the organ. 
(//) Red blood-corpuscles are frequently found in the vesicles in greater or less 
number and in various stages of disintegration and decolorisation. 
In the epithelial wall of vesicles containing red blood-corpuscles, granules of yellow 
