1892-93.] Dr Whiting on Histology of the Spleen. 
21 
On the Comparative Histology and Physiology of the 
Spleen. By Arthur J. Whiting, M.D. 
(Read January 10, 1893.) 
{Ahstmd.) 
The principal subject of the author’s research has been the com- 
parative histology of the spleen in twenty-two different kinds of 
animals, embracing all the typical vertebrates from the fish to Man. 
The capsule of a typical mammalian spleen, such as that of the 
cat, consists of two layers, the outer composed of ordinary fibrous 
tissue, the inner of nonstriped muscle. The splenic artery and 
vein, as they enter the organ at the hilum, are enclosed in a 
sheath formed by an inflexion of the capsule, and, like it, consisting 
of a fibrous and a muscular layer, the fibrous layer being next the 
vessels, and the muscular layer external to it, adjoining the pulp. 
This perivascular sheath may be termed the hilar sheath of the 
vessels. The muscular layer of the capsule sends inwards a ramify- 
ing system of cord-like trabeculae consisting of non-striped muscle 
that join the muscular layer of the hilar sheath and form a contrac- 
tile framework for the organ. 
The principal variation in the supporting framework of the spleen 
in different classes of animals is in two directions — in the degree of 
its muscularity, and in the degree of development of the trabecular 
system. INTon-striped muscle was found in the framework of all the 
spleens examined. At its minimum in fishes, it gradually increases 
in amount as the scale is ascended through the amphibia, the 
reptiles, the birds, to the mammals, and reaches its maximum in the 
ungulata or in the carnivora. 
A trabecular system proper was found in mammals alone, most 
highly developed in the carnivora, and least in the cetacea. 
After the artery and vein have run together for a short distance 
into the interior of the spleen invested by the hilar sheath, they 
separate, the veins branch off along the trabeculae, while the arteries 
continue their course branching dichotomously within the hilar 
sheath. But after separating from the vein they become enveloped 
