or THE THYROID GLAND OF THE DOG. 
561 
methods, the characters and distribution of the lymphatics within the gland were found 
to be as follows : — 
Traversing the gland, chiefly in a longitudinal direction, and accompanying the larger 
blood-vessels and septa of connective tissue, are numerous lymphatic vessels of consider- 
able size. They not uncommonly surround the arteries which they accompany, as repre- 
sented in Plate 47. fig. 1, and even completely invaginate them, so as to represent “ peri- 
vascular lymphatics ” (see fig. 5). These vessels are in direct connexion with the network 
of lymphatics already described on the surface of the organ (see p. 559). They are pro- 
vided with valves ; and their walls are formed by a layer of endothelium, the cells of 
which are elongated and have a somewhat sinuous outline. Many of these cells appear 
to be provided with two, or even three, oval-shaped nuclei (see fig. 7). The endothelial 
markings are well seen in specimens prepared according to method 2, and the nuclei 
sometimes assume a faint violet tint from the haematoxylin. 
As represented in figure 7, the nuclei are not uncommonly seen as if lying under the 
silver line separating two adjacent cells, a part of the nucleus being on one side of the 
line and part on the other. 
Coming off from these vessels, and traversing the gland in all directions, are numerous 
lymphatic tubes of very varied size and shape. The larger ones run principally between 
groups of vesicles, and are in direct communication with smaller ones which pass between 
individual gland-vesicles. The latter (the “ few finer canals ” of Frey), in a well-injected 
specimen, are seen to be numerous, and are frequently noticed partially, and not uncom- 
monly completely, surrounding the individual vesicles. As mentioned, these tubes vary 
very much in size and form — in fact, they appear to adapt themselves accurately to the 
intervals left between the vesicles. This being the case, as might be expected,' the dia- 
meter of a tube rarely remains constant for any distance ; and where the intervals left 
between the vesicles are larger, the tubes expand into lymphatic spaces having the most 
irregular shape. 
The lymphatic tubes, then, both large and small, together with the lymphatic spaces, 
form a dense rounded network of freely anastomosing canals, which permeates the entire 
substance of the thyroid gland. In no case have I seen any indication of the lymphatics 
terminating in blind extremities , and can only attribute such an appearance to an imper- 
fect injection. The distinctly tubular character of the tubes, as well as the form of the 
spaces and tubes generally, are best seen in specimens injected with Berlin blue (figs. 
2 & 3). In perfectly injected parts of silver preparations a continuous layer of endo- 
thelial cells is seen lining both larger and smaller lymphatic tubes and lymphatic spaces. 
Figs. 4 & 6 represent lymphatic tubes and spaces lined by the endothelium, which in 
some places has been accidentally cut away. 
The endothelial cells are somewhat elongated, and present an irregularly sinuous out- 
line. They form a delicate membrane, adhering closely to the outer wall of the vesicles. 
In a thick section this can be well seen following accurately the walls of the vesicles, and 
covering them, as it were, like a thin veil. (Attempts to represent this disposition of 
