COMPARATIVE HISTOLOGY AND PHYSIOLOGY OF THE SPLEEN. 273 



In the spleen of the Porpoise there does not seem to be anything corresponding 

 to the ellipsoids, and in the Narwhal the terminal arteries are merely invested by a 

 somewhat thick fibrous sheath that contains a few lymphoid cells. 



In the spleen of the Rabbit the arteries, after leaving the follicles, are invested by 

 a continuous fibro-cellular " ellipsoidal sheath." The fibres are usually spindle-shaped, 

 and are arranged both longitudinally and concentrically. Within long meshes formed 

 by them, lymphoid cells are found. There is an indistinct blood-sinus at the periphery 

 of the sheath, something like that in the tortoise and rook. In the Rat and Mouse 

 there is a similar ellipsoidal sheath, which is, however, surrounded by a well-marked 

 blood-sinus. In the Guinea-pig a similar sheath forms septa between some of the 

 large sinuses of the pulp. 



In the Hedgehog the ellipsoids are numerous and conspicuous. In transverse 

 section they are round ; in longitudinal section they are seen to be oval, or not 

 unfrequently trilobed. The vessels are arranged as in the dog and cat. The axial 

 vessel has a distinct circular coat consisting apparently of delicate muscle fibres 

 placed at long but regular intervals from each other. The substance of the ellipsoids 

 consists of a considerable amount of a granular ground substance, in which are 

 imbedded numerous clear, uninucleated lymphoid cells, and of an ill-developed 

 fibrous reticulum that contains many concentrically arranged spindle cells, which 

 are in all probability muscular. There is a well-developed external layer composed 

 of strong fibres having long nuclei, which are almost certainly muscular. Surrounding 

 the ellipsoid is a somewhat narrow venous sinus. 



In the Human Spleen after the arteries leave the follicles they are continuously 

 invested by a fibro-cellular ellipsoidal sheath as in the spleen of the Rodents. It is 

 composed of a network of strong connective tissue strands which, near the periphery, 

 is denser and composed of fibres arranged mainly longitudinally, and in the meshes 

 of this network are some lymphoid cells. At first the sheath is about twice the 

 thickness of the diameter of the vessel, but as the artery becomes smaller, the sheath 

 becomes thinner ; the lymphoid cells decrease in number until they practically disappear, 

 while the fibres persist so as to form a longitudinal sheath until the vessel opens into 

 the spaces of the pulp. 



Commentary. 



The ellipsoids were first noticed by Billroth # in the spleen of the bird, and have 

 since been described by Schweiggek-Seidel^ under the name of the capillary sheath, 

 in the pig, dog, and cat, later in the same animals by W. Muller J and Kyber,§ and 

 still later by Pouchet|j in the Selachian cartilaginous fish. Since the preceding 

 observations were made they have been described by Dr Bannwarth 1F in the spleen 

 of the cat, and, as we can testify, with fulness and accuracy. He has, however, failed 



* Billroth (8), p. 97. t Schweigger-Seidel (10), p. 465. t W. Muller (12), p. 360. 



§ Kyber (13), p. 561. j| Pouchet (18), p. 498. 1 Bannwarth (26), p. 398. 



