DR. H. WATNEY ON" THE MINUTE ANATOMY OP THE THYMUS. 1081 
lymphoid cells, such as are found in the lymphatics. These considerations point out 
that the cortex of the follicle is the more important and essential part of the thymus. 
The Lymphatics of the Thymus. 
The capsule of the follicle surrounds the cortical portion, separating the cortical-tissue 
from the projections of interfollicular-tissue, such as are shown at ct', in Plate 83, 
figs. 1 and 2 and Plate 86, fig. 10. In sections of the thymus, the capsule is seen to be 
composed of endothelial cells; blood vessels penetrate it obliquely, and, supported by 
it, enter the follicle (see Plate 87, fig. 25). The capsule in certain stages of involution 
contains much fibrous tissue and some cells ; but in the majority of cases it appears as 
a double membrane, whose outer wall is also the wall of a lymphatic space. These 
lymphatic spaces contain many thymic corpuscles. It is however possible that some 
of these cells have passed into the lymphatic spaces in making the specimen. 
It was not found possible to discover any lymphatic vessels in the follicles, and none 
can be shown to exist in the cortex of the follicle during the period of the full develop¬ 
ment of the gland; as no lymphatic vessels can be seen in sections, and there are no 
perivascular sheaths to the vessels (see Plate 87, figs. 25 and 26). In the medulla many 
of the vessels, even in the early stages of the growth of the thymus, have perivascular 
sheaths ; and during involution almost all the vessels of the medullary portion 
(see Plate 94, fig. 96) and many even of the vessels of the cortex, are surrounded by 
perivascular spaces. These spaces may act as lymphatic vessels. It is seen from the 
foregoing description that the cortical part of the follicles—the more important part— 
has nothing which can serve as a lymphatic vessel, during its greatest development, 
except the lymphatic space on the outer side of the capsule. 
The course of the lymphatics issuing from the thymus was traced in the Calf. The 
young animals were killed by chloroform, and, as soon as dead, a small quantity of a 
saturated solution of indigo-carmine was injected by puncture into the thymus, the 
small wound in the skin was closed up, and the animals were left for half-an-hour. It 
was found that the indigo-carmine solution passed into the lymphatic vessels, travelled 
along them, and marked them out, so that they could be easily followed by careful 
dissection. 
In the neck part of the thymus the blue fluid is seen to leave the organ by a number 
of small vessels running by the side of the minute veins. These small lymphatic 
vessels form the afferent vessels of small glands lying in the neck on each side of the 
thymus ; from these glands the efferent lymph-vessel runs down the neck, not far from 
the large lymphatic trunk, but never joins it, and can be traced to two other lymphatic 
glands lying on the trachea, close to its point of entrance into the thorax. It will be 
noticed that the lymphatic vessels do not run longitudinally in the gland, and that 
there is no large lymphatic vessel running at the back of the isthmus of the thymus, 
as described by His (46). 
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