158 SPECIAL HISTOLOGY. 



from the interior of the spleen, to be distributed in its coats, and 

 open into the superficial trunks. The latter may readily, in the 

 Ox, be traced for a certain distance into the interior, so far that 

 it can be seen that they not only at first, but subsequently, 

 always accompany the arteries. Their origin is unknown, and 

 I can only say, that in the Malpighian corpuscles and in the 

 penicilli, as microscopic investigation shows, the arteries are no 

 longer accompanied by lymphatics. They probably, as in the 

 liver, belong only to the vascular sheaths. In structure, the 

 splenic lymphatics present no peculiarities, and they have valves. 

 The arteries in the human spleen are exceedingly muscular, 

 which sufficiently explains the dilatation and subsequent con- 

 traction of the organ observed 5 or 6 hours after the ingestion 

 of food, noticed by many observers. In animals, besides these 

 contractile elements, the muscles of the coats and trabecules 

 which I have discovered, may take some part in this process, 

 and their presence further accounts for the circumstance that 

 the spleens of Animals contract by galvanism, while that of man 

 does not (vid. Mikr. Anat. II, 2, p. 265).] 



§ 170. 



Physiological remarks. — The spleen is developed at the end 

 of the second month, in the foetal mesogastrium, at the fundus 

 of the stomach, from a blastema which, derived from the middle 

 layer of the germ, independently of the stomach, the liver, 

 or the pancreas, collects in this situation. It is, at first, a 

 whitish, often slightly lobed body (072'" in length, 04'" in 

 breadth, in the ninth to the tenth week), which gradually be- 

 comes red and is very soon as rich in blood and in vessels as 

 in the adult. The roundish small cells, of which the spleen is 

 at first entirely constituted, become, in the third month, partly 

 developed into vessels and fibres, whilst another portion remains 

 as parenchyma-cells. The Malpighian corpuscles are not formed 

 till subsequently, but may always be found at the end of the 

 foetal period, although considerably smaller than afterwards. I 

 do not know how they are formed, but I presume that they 

 proceed from simple masses of cells, whose external elements 

 become metamorphosed into the coat of connective tissue, whilst 

 the internal ones, partly persisting in their original condition, 

 partly becoming metamorphosed into vessels, form the contents. 



