580 
MR. E. C. BABER ON" THE STRUCTURE OF THE THYROID GLAND. 
point of their convergence. In quite small Frogs the thyroid gland appears in trans¬ 
verse sections as a somewhat flattened body, lying on the ventral surface of the hyoid 
cartilage, partly between it and the hyoglossus muscle. In rather larger Frogs it 
presents in transverse section a somewhat triangular outline (see Plate 68, fig. 1, i, i), 
the base being applied to the ventral surface of the cartilage (Plate 68, fig. 1, i) and 
the apex projecting forwards by the side of the hyoglossus muscle. In still larger 
Frogs transverse sections show that the gland often extends forwards, but its develop¬ 
ment on the two sides appears to be irregular and unsymmetrical. In Frogs of full 
size it may, however, still be found flattened and extending very slightly forwards. 
I may here mention that the structure of this gland resembles that of the thyroids 
of other animals. It consists of numerous vesicles separated by a stroma of connective 
tissue, the whole being surrounded by a capsule of similar character. The vesicles are 
lined by a single layer of cubical or slightly columnar epithelial cells, which are devoid 
of dark pigment. It will be seen that the results of these observations on the Frog 
agree on the whole with those of W. Muller. 
Pisces .—In the Skate, as far as I have seen, the gland is single (with the exception 
of a few detached vesicles) and forms a yellow flattened, lobulated body, occupying the 
median line at the bifurcation of the branchial artery.* Anteriorly it sometimes 
presents a narrow process of gland-tissue running forwards, and behind it is limited by 
the bifurcation of the branchial artery. The vesicles of the gland, of various sizes, are 
distinctly visible to the naked eye. In the Conger Eel the gland occupies a similar 
position and forms a reddish flattened body. 
METHODS EMPLOYED. 
Methods of Injection. 
I. The gland of a freshly-killed animal was injected in situ with a solution of Berlin 
blue by the method of puncture. The gland being hardened first in a mixture of 
equal parts of methylated spirit and water, and afterwards in methylated spirit, and 
sections mounted in dammar or balsam in the usual way. 
II. The fresh gland was injected in a similar manner with •§- per cent, solution of 
nitrate of silver in water and hardened as before. 
III. The fresh gland was injected in situ by the method of puncture with per cent, 
solution of osmic acid in water. The gland being removed was cut up into small 
pieces, and these placed in solutions of the same acid ranging in strength from -fo to 1 
per cent, for periods ranging from 1 to 24 hours. The gland being subsequently placed 
in alcohol and sections mounted in glycerine or in dammar. 
* Handfield Jones (quoted by Owen, loc. cit .) has observed in the Skate a second body of similar 
structure situated some distance behind this. I have not observed this second gland, but cannot deny its 
existence. 
