260 DE A. J. WHITING ON THE 



the rule in being relatively more muscular than the capsule. The hilar sheath is 

 well developed. Its outer portion is somewhat strongly muscular. The muscle fibre 

 cells are arranged both longitudinally and transversely. 



Summary regarding the Supporting Framework of the Spleen. 



1. The variation in the supporting framework of the spleen appears to be mainly 

 in two directions, one in the degree of its muscularity, and the other in the degree of 

 the development of the trabecular system. 



2. I would here emphasise the fact that the hilar sheath around the vessels is 

 muscular as well as the trabecular, and, as I have several times already implied, its 

 muscularity varies with that of the capsule as a whole, and is therefore in the aggregate 

 less than that of the trabecular, which resemble the deeper muscular portion of the 

 tunica propria. Klein * and Bannwarth t have noticed the presence of muscle in the 

 hilar sheath. 



3. As the supporting framework of the spleen becomes less strongly developed in 

 the higher animals, and as its muscularity decreases, the elastic element increases. 



4. I think it is important to regard the hilar sheath as outside the essential splenic- 

 substance, as, in fact, an inflection of the capsule. 



5. The trabecular system proper appears to be peculiar to the Mammalia ; where it is 

 represented in the lower vertebrates it probably corresponds with the hilar sheath and, 

 except in the Ophidia, is feebly developed. 



6. Among mammals the trabecular system reaches its highest development, as far as 

 I have observed, in the Carnivora ; its lowest, in the Cetacea. 



7. Unstriped muscle occurs in the framework of all the spleens that I have examined. 

 At its minimum in the fish, it gradually increases in amount as the scale is ascended 

 through the amphibians, the reptiles, the birds, to the mammals, and reaches its maximum 

 among the Mammalia in the Ungulata or Carnivora, then gradually decreases through the 

 Cetacea and the Eodentia (rising slightly, however, in the hedgehog) to Man. 



Chapter II. 



The Adenoid Sheath of the Splenic Arteries and the Splenic Follicles.\ 



As the splenic artery and nerves pass through the hilus of the spleen they are 

 ensheathcd by the inflected capsule. The sheath consists of three strata : next the artery 

 is a thin layer of loose areolar tissue, derived, in part at least, from the subperitoneal 

 connective tissue, and probably in part from the tunica adventitia of the artery, contain- 

 ing a few lymphoid cells ; then comes a layer of denser white fibrous tissue, derived from 

 the outer layer of the capsule, containing a considerable number of connective tissue 



* Klein (10), p. 3C7. t Bannwarth (26). 



X The following general description is based on the examination of the spleen of the Kitten. 



