360 THE SPLEEN, BY WILHELM MULLER. 



Tomsa, they penetrate the cytogenous sheaths of the vessels 

 and their circumscribed enlargements, forming a plexus which, 

 near the periphery of these structures, is only incompletely 

 surrounded by the cavities of the adjoining pulp. 



NERVES OF THE SPLEEN. The nerves of the spleen also 

 accompany the arteries in their course. They consist chiefly of 

 Remak's fibres. They appear, in part at least, to terminate in 

 peculiar organs that invest the capillary terminations of the 

 vessels (W. Miiller). These organs form ellipsoids, in the long 

 axis of which a single capillary vessel runs. The substance of 

 the ellipsoid consists of a pale, very finely granular substance 

 in which oblong nuclei are imbedded (Schweigger-Seidel and 

 W. Miiller). These are highly developed in the spleens of 

 Birds and carnivorous animals, but are only rudimentary in 

 those of Rodents and of Man. In the interior of their granu- 

 lar mass fine fibres of Remak occur, the mode of termination of 

 which has not as yet been actually determined. They require 

 further investigation. 



DEVELOPMENT OF THE SPLEEN. In all Vertebrata the spleen 

 proceeds from a segment of the peritoneum. The situation of 

 this segment differs in the several classes. In Ophidia it is the 

 peritoneal investment of the upper extremity of the pancreas ; 

 in Fishes, Frogs, and Chelonia, it is the mesentery of the small 

 or large intestine ; in the Salamanders, Lizards, Birds, and Mam- 

 mals, it is a prolongation of the mesogastrium from which the 

 organ is developed. Its first appearance occurs in the form of 

 a homogeneous thickening of the peritoneum, caused by in- 

 crease of the embryonic formative cells of which it is composed. 

 This thickening occurs very early in Man ; it is already demon- 

 strable at the period when the first budding out of the pancreas 

 has made its appearance. At this time bloodvessels may be fol- 

 lowed to the seat of the rudiment of the spleen (W. Miiller).* 

 At this period there may be observed in chromic acid preparations 

 a very delicate pale network intervening between the embryonic 



* Their relation to the first appearance of the spleen requires further 

 investigation. 





