1 



1 1 4 NORMAL HISTOLOGY. 



the peritoneal folds at which the splenic vessels and nerves enter or leave the 

 organ, the outer surface of the capsule is united with the serous membrane, 

 the peritoneum, which almost completely invests the spleen. At the hilum 

 the tissue of the capsule is continued into the organ and supports the blood- 

 vessels and nerves. The capsule, furthermore, gives off from its deeper sur- 

 face numerous processes, the trabecula, which pass into the substance of the 

 organ and break up into innumerable delicate prolongations that unite to 

 form the supporting fibrous framework. This framework is arranged with 

 a certain degree of regularity, since the trabeculae subdivide the spleen, at 

 least its peripheral zone, into fairly regular compartments, the splenic lobules 

 of Mall, about i mm. in diameter. Each of these units is imperfectly 

 defined by three intejlobular trabecula, from which secondary intrglobular 



Capsul 



Splenic 

 pulp 



FIG. 154. Section of spleen under very low magnification, showing general arrangement of splenic 



tissue. X 10. 



processes penetrate the lobule and subdivide the latter into about ten primary 

 compartments. These, as well as the lobules themselves, are not isolated, but 

 freely continuous, since the intervening trabeculse and processes form only 

 incomplete partitions. The spaces within the fibrous framework are filled 

 with the highly vascular lymphoid tissue, known as the splenic pulp. 



The relation of the blood-vessels to the splenic lobules, although com- 

 plex, is very definite. The branches of the splenic artery, after entering at 

 the hilum and running some distance within the trabeculae in company with 

 the larger veins, break up into smaller vessels, each of which, parting from 

 the vein, enters the proximal end of a lobule, through the middle of which it 

 courses, giving off twigs, one for each primary compartment of the lobule. 

 On leaving the trabeculae, the arteries carry with them prolongations of con- 

 nective tissue, which, with the adventitiae of the vessels, surround the latter 

 with fibro-elastic coats of considerable thickness. Within these envelopes 

 local accumulations of lymphoid cells (lymphocytes) occur and in conse- 

 quence the arteries are surrounded by spherical or fusiform masses of dense 



