MR. E. C. BABER ON THE STRUCTURE OF THE THYROID GLAND. 001 
possess the following structure (see Plate 69, fig. 20). They consist of a solid mass of 
more or less cylindrical rows of cells (Plate 69, fig. 20 i, i, i) which are much con¬ 
voluted and interlace in all directions. Between them run capillary blood-vessels and 
also probably some lymphatics. These “cylinders” are composed of cells resembling 
epithelial cells, columnar or cubical in shape, those on the surface of the cylinder, next 
to the capillaries, being arranged at right angles to those vessels (Plate 69, fig. 20, 3 ). 
Each cell is provided with a nucleus usually oval in shape. In very few, if in any, of 
these cylinders have I been able to detect any central canal. In Dogs aged three 
months and upwards I have usually observed these “undeveloped portions” as distinct 
bodies, not continuous with the normal gland-tissue, but separated from it by layers 
of connective tissue, and frequently lying in depressions on the surface of the gland 
(see Plate 69, fig. 19). They appear to be portions of gland whose development has 
become arrested at an early stage, and there was in these Dogs, usually, no evidence 
to show that these bodies were undergoing any further development. Exceptions to 
this, however, occur ; for example, in a male Dog (aged nearly 2 years) an “ undeveloped 
portion” was found which was not distinctly separated from the rest of the gland- 
tissue, and contained well-formed vesicles showing that it was undergoing further 
development. 
In the Kitten similar undeveloped portions are seen, which are sometimes observed 
to be continuous with the ordinary gland-tissue. In this case a formation of vesicles 
from the cylinders of cells appears to be taking place by the growth into them laterally 
of processes of connective-tissue with blood-vessels, and by their excavation into 
vesicles. In the Kitten the cylinders are less convoluted than in the Dog, and 
throughout the gland the fully-formed vesicles frequently appear grouped in rows, 
which have a more or less parallel arrangement. 
“ Undeveloped portions” have also been observed in the thyroid glands of the 
Sheep, Seal, and Book. In the Seal there was a large quantity of fibrous tissue 
between the cylinders, as well as between the vesicles in the ordinary gland-tissue. 
Somewhat similar, but much shorter, cylinders of cells have been seen in the thyroid 
gland of the Pigeon scattered throughout the gland. 
There can be no doubt that these bodies are portions of the gland of which the 
development has progressed no further than the stage described by W. Muller (vide 
supra, p. 583), in which the gland consists of a network of cylindrical tubes, at first 
irregular, but afterwards becoming more regular in character ; the tubes (according 
to Muller) being composed of short cylindrical epithelial cells, placed radially on the 
surface of the envelope and being at first solid, but subsequently provided with a 
lumen. I have also observed these cylinders in the thyroid glands of foetal Pigs 
(measuring about 2^ inches in length). The occurrence of these undeveloped portions 
continuous with the ordinary gland-tissue in the thyroids of young animals of course 
merely indicates that a formation of gland-tissue is taking place in the manner 
described by W. Muller. 
4 1 
MDCCCLXXXI. 
