1082 
DR. H. WATNEY OH THE MIHIJTE ANATOMY OF THE THYMUS. 
The indigo-carmine solution, if injected into the thoracic portion of the thymus, can 
he traced to lymphatic glands lying in the thorax, generally to one gland lying on the 
arch of the aorta, and from thence to the large veins on the left side. There seems to 
be no intercommunication between the lymphatics of the thorax and of the neck. 
The Blood Vessels. 
The most noticeable fact about the blood vessels of the thymus, in an injected speci¬ 
men (see Plate 85, fig. 6), is the disposition of the large vessels in two rings :—(l) They, 
to a great measure, surround the follicle, more so, usually, than in Plate 85, fig. 6 ; 
and (2) form nearly a complete circle on the margin of the medullary portion of the 
follicle. This latter circle is not, however, outside the medulla, but situated within it, 
or just on its borders. This disposition of the vessels is true of all cases where the 
follicle is polygonal,, and contains one medullary centre. "W here there are two 
medullary portions there are two central rings of vessels, or if the medulla be in 
the form of long processes, the surrounding vessels run longitudinally. The ring of 
vessels surrounding the follicle is composed of arteries and veins, which give off or 
receive branches from two neighbouring follicles. The inner circle, or circles, is also 
composed of arteries and veins, but chiefly of the latter. The cortex is thus surrounded 
by large vessels running parallel to its inner and outer surfaces, and is chiefly supplied 
with arterial blood from the outer circle of vessels, while the inner circle collects the 
venous blood from the cortex and from the medulla. In the cortical portion fine 
capillary vessels are met with, the majority of which run in a radiating manner from 
the exterior inwards. There are, however, a few vessels penetrating the cortex from 
the arteries in the medulla, and sometimes vessels from outside run in loops, and join 
the veins on the outside. 
The medulla, in injected specimens of the thymus, is more vascular than the cortex, 
on account of the ring of large vessels which it contains. The blood supply of the 
interior of the medullary portion varies as follows : When the thymus is in a state of 
growth, or during full development, the vessels in the interior of the medulla are few 
and fine, there being often one or more small central arteries; those parts of the medulla 
which contain the granular cells and the concentric corpuscles have very few and only 
small vessels (see Plate 85, fig. 6). In the thymus during involution, on the contrary, 
the vessels of the medulla are numerous and very large, often surrounded by comiective 
tissue, and have perivascular sheaths. The large veins of the medulla, as has been 
described, pass out of the follicle in the bands of connective tissue which invade the 
cortex (see Plate 83, figs. 1 and 2 ; and Plate 85, fig. 6, V'), and help to form the 
large veins running between the follicles. 
Extravasations take place in injected specimens if the pressure used is at all high. 
These extravasations occur only in the medullary portion; and the fluid, if it be 
carmine and gelatine, is found, as a coloured reticulum, between the cells. 
