222 OF ABSORPTION AND SANGUIFICATION. 



much care by Mr. 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 fourth and fifth 

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

 canal to the spine (the " mesogastrium "), as a small whitish mass of blas- 

 tema, perfectly 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 de- 

 veloped between the eighth and ninth days: the former as a thin membrane 

 composed of nucleated fibres; the latter consisting of similar fibres, which 

 intersect this organ at first sparingly, and afterwards in greater quantity. 

 The bloodvessels of the 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 Suprarenal 

 and Thyroid bodies in their earliest stages of evolution ; consisting of nu- 

 clei, nucleated vesicles, and a fine granular plasma. Peremeschko 2 and 

 Cohnheim 3 have also noticed peculiar arnoebiform cells or protoplasmic 

 bodies to be constantly present in the embryonal spleen, and in the splenic 

 pulp, but their function is unknown. When the splenic vessels are being 

 formed, many of the above-mentioned nuclei are surrounded by a quantity 

 of fine dark granules, arranged in a circular mode; and these appear to be 

 developed into nucleated vesicles, of which, when the splenic vein is formed, 

 nearly the whole pulp is composed ; the nuclei of these subsequently break 

 up into a mass of granules, which fill the cavities of the vesicles. The Mul- 

 pighian corpuscles are developed in the pulp at the angles of division of 

 the smaller bloodvessels, by the aggregation of nuclei into circular masses, 

 around which a fine membrane is subsequently fo'rmed. Thus during foetal 

 life we have evidence of a process of cell-growth and maturation, followed 

 by cell-destruction, in the colorless parenchyma. The largest proportional 

 size and the greatest functional activity of the Spleen, however, seem to be 

 exhibited during adolescence and the most vigorous period of adult life, its 

 proportionate weight to the whole body being then as 1 : 320 or 400. 



159. The Suprarenal bodies in Man and most Mammalia present, like the 

 kidneys, a division into cortical and medullary substances ; the inner por- 

 tion of the former having a remarkably dark-brown hue. The cortical sub- 

 stance, divided by Arnold into three zones, named Z. glomerulosa, fascicu- 

 lata, and reticularis, is principally formed of a stroma of connective tissue, 

 so arranged as to leave a series of oval spaces lying end to end with some 

 indistinct indications of a tubular structure; the spaces or tubes are filled 

 with a finely granular plasma containing a large number of fat-part .ides, 

 nuclear corpuscles, and cells, some of which are small, spherical, or cubical, 

 with large nuclei and finely granular contents, whilst others are large, 

 coarsely granular, with indistinct nuclei, and much fat in their interior. The 

 medullary substance consists of a basis of fibrous tissue which is continuous 

 with processes that come off from the sheath of the cortical substance, and 

 supports a plexus of tubes filled with finely stellate or polygonal granular 

 cells, together with numerous bloodvessels and nerves. 4 Holm, in the 



1 On the Development of the Ductless Glands in the Chick, in Philosophical Trans- 

 actions, 1852, p. 2!)5; sec also his Pri/.c Essay 



! Wicn Acad. Sit/.uii^st. <T., 18';?, Kd Iv and Ivi. 



3 Virchow's Archiv, Hd. xxxiii, p. 311. 



4 See Art. Suprarenal Capsule in Cyclop, of Anat. and Phyi-iol., vol. iv ; Kollikrr, 



