Jeremiah 8. Ferguson 69 
The writer has observed that the formation of such heavy ridges as 
those shown in Fig. 3, nearly always occurs at those points where the 
vessel branches. It is possible that, as in the case of the somewhat similar 
ridges in the veins of the erectile tissues (see Kolliker’s Handbuch der 
Gewebelehre, 6te Aufl., 1902, pages 486 and 487), these muscular pro- 
tuberances may to some extent serve the purpose of valves. 
As the large central veins approach the hilum of the organ they form 
still larger vessels which partake of the structure of the suprarenal vein. 
The point of transition from the one type to the other is variable, occasion- 
ally the type of the large central veins is continued to the exit of the 
suprarenal vein at the hilum of the organ. More frequently the primary 
branches of the suprarenal vein may be traced for a considerable distance 
into the medulla of the organ, still retaining the type of structure found 
in the larger vessel. 
The suprarenal vein presents three coats, intima, media, and adventitia. 
The tunica intima, in addition to its endothelial lining, possesses a thin 
membrane of very delicate connective tissue in which occasional branched 
connective tissue cells may be distinguished ; such cells are, however, very 
scanty. This coat also contains a delicate network of elastic fibers. 
The tunica media of the suprarenal vein is extremely thin, rarely ever 
does it exceed in thickness the tunica intima. It consists chiefly of 
fibro-elastic tissue, the elastic fibers forming quite a dense network. 
Few muscle fibers occur in this coat, nowhere are they found in sufficient 
numbers to form a definite layer, as in veins of similar size in other 
organs. Some of the muscle fibers are circularly disposed, but many of 
them are longitudinal. 
The tunica adventitia is by far the thickest of. the three coats and 
forms two-thirds to five-sixths of the entire vascular wall. It consists 
chiefly of smooth muscle fibers, all of which are longitudinally disposed. 
These smooth muscle fibers form characteristic coarse bundles which are 
distributed around the entire circumference of the vessel. The largest 
of these bundles may occasionally form projecting ridges as in the smaller 
veins, but as a rule the muscular tissue is more evenly distributed than in 
the central veins. Each of the muscle bundles is enveloped in a peri- 
mysial sheath of connective tissue, which blends with that of the tunica 
media. These adventitial sheaths possess a dense network of elastic 
fibers, in fact the greater part of the elastic tissue in the vascular wall 
is frequently found in the adventitia. On its outer surface the tunica 
adventitia is continuous with the capsule of the adrenal or with the 
adjacent connective tissue. 
This peculiar type of vessel is not strictly confined to the suprarenal 
