458 OF ABSORPTION AND SANGUIFICATION. 



that the idea long entertained as to their dilatation into cavernous spaces or 

 sinuses is incorrect, so far as the Human spleen is concerned; and that there is 

 nothing peculiar in their distribution, save in their mode of ramification, which 

 closely resembles that of the arteries, and in the absence of valves. In the spleen 

 of the Ox, however, and of other Ruminants a true cavernous structure does 

 exist. * 



VI. The Lymphatics of the Spleen are few and inconsiderable in Man ; being 

 less numerous than in other glandular organs, such as the liver and kidneys. 

 In some of the lower animals they are more abundant ; but even here they are 

 mostly superficial, and scarcely penetrate to the interior of the organ. 



Vii. The Nerves of the Spleen are apparently very large in some animals, 

 especially in the Ruminants; but the great size of their trunks and branches is 

 chiefly due to the large proportion of ordinary fibrous tissue which enters them; 

 the number of real nerve-fibres being extremely small. 



483. The history of the development of the Spleen, which has been recently 

 studied with great care by Mr. H. Gray, 1 presents facts of great interest, as 

 aiding in the determination of the functional character of this organ, and of the 

 nature of its component parts. It arises in the Chick between the 4th and 5th 

 days of incubation, in a fold of membrane which connects the intestinal canal 

 to the spine (the "intestinal lamina"), as a small whitish mass of blastema, per- 

 fectly distinct from both the stomach and the pancreas; from the former of 

 which it has been said by Bischoff, and from the latter by Arnold, to take its 

 origin. The external capsule and the trabecular tissue are developed between 

 the 8th and 9th days; the former as a thin membrane composed of nucleated 

 fibres, the latter consisting of similar fibres which intersect the organ at first 

 sparingly, and afterwards in greater quantity. The bloodvessels of this organ 

 are formed within itself, independently of those which are exterior to it ; and 

 blood-corpuscles are also observed to originate in the substance of its blastema, 

 their formation continuing until its connection with the general vascular system 

 is completed, at which period their development appears to cease. The pulp- 

 tissue, at an early period of its formation, closely corresponds with that of the 

 supra-renal and thyroid bodies in their earliest stages of evolution ; consisting of 

 nuclei, nucleated vesicles, and a fine granular plasma. When the splenic vessels 

 are formed, many of these nuclei are surrounded by a quantity of fine dark granules 

 arranged in a circular form; and these increase up to the time when the splenic 

 vein is formed, when nearly the whole mass is composed of nucleated vesicles, 

 the nuclei of which gradually break up into a mass of granules which fill the 

 cavities of the vesicles. The Malpighian vesicles are developed in the pulp, by 

 the aggregation of nuclei into circular masses, around which a fine membrane 

 soon appears, in a manner precisely similar to those of the supra-renal ( 485) 

 and thyroid 'bodies. 



484. The Supra-Renal bodies in Man and most Mammalia present, like 

 the kidneys, a division into cortical and medullary substances ; the former 

 having a lighter hue than the latter. The cortical substance is principally 

 formed of closed vesicles, which are arranged in linear series (so as to present 

 the appearance of radiating tubes), and which are united by ensheathing coats, 

 derived from processes of the fibrous envelop. According to Ecker, 3 who is 

 confirmed on this point by Frey, 3 these vesicles always remain distinct ; but Mr. 

 Gray appears to think that there is sometimes an absolute coalescence between 

 them ( 485). The diameter of the vesicles varies from about 1-1 500th to 

 l-800th of an inch ; and some of them have a length of from l-650th to l-480th 



1 " Proceedings of the Royal Society," Jan. 15, 1852. 



2 " Annales des Sciences Naturelles," Aug. 1847. 



3 "Cyclopaedia of Anatomy and Physiology," Art. "Supra-renal Capsules." 



