THE SPLEEN. 



1783 



gastric or renal surface, more often the former, or it may appear simply as a knob at 

 the inner side of the lower end. This knob, the infe7-ior tubercle, is usually more or 

 less evident at the termination of the intermediate border. 



Structure. — In addition to the serous covering contributed by the peritoneum, 

 the spleen is completely invested by a distinct capsule, or tunica albuginea, composed 

 of dense bundles of hbrous tissue, numerous elastic fibres, and, in its deeper layer, 

 sparsely distributed bundles of involuntary muscle. At the hilum the tissue of the 

 capsule is continued into the organ, supporting the blood-vessels and nerves. The 

 capsule likewise gives off numerous trabeculce which pass into the substance of the 

 gland and break up into innumerable delicate processes which unite to form the sup- 

 porting framework. 



Mall ^ has shown that this framework is arranged with greater regularity than was 

 formerly recognized, since the trabeculae subdivide the spleen into fairly regular com- 

 partments, the splenic lobules, measuring about i mm. in diameter. Each of these 

 units is bounded by three interlobular trabeculce, from which secondary intralobular 

 processes penetrate into the lobule, whereby the latter is subdivided into about ten 

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



Fig. 1505. 



Capsule 



Interlobular veiti 



Malpighianbod\ 



Splenic pulp 



yjf / r -^ j?F '^K^-i*^. ' f ^ W'- •Jti'^P^'^ ..trabi 



iterlobular 

 trabecula and 

 vein 



Splenic pulp 



Interlobular 

 trabecula 



Section of spleen under very low magnification, showing general arrangement of splenic tissue. X 10. 



but freely communicate, since the intervening trabeculae form only incomplete parti- 

 tions.- The spaces within the fibrous framework are filled with the highly vascular 

 lymphoid tissue constituting the splenic pulp. 



The relation of the blood-vessels to the lobules of the spleen is, according to 

 Mall, very definite. The branches of the splenic artery, after entering at the hilum 

 and running for some distance within the trabeculae, break up into smaller vessels, 

 each of which enters the proximal end of the lobule, through the middle of which it 

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

 The lymphoid tissue occupying the compartment is arranged as anastomosing cylin- 

 drical masses, the pulp-cords. Within the latter course the terminal branches of the 

 splenic arteries, while outside and between the cords lies the plexus of venous spaces 

 from which the more definite channels, the intralobular veins, arise. The terminal 

 arteries within the pulp-cords give off numerous small branches which terminate in 

 minute expansions, the ampullce of Thoma. The latter communicate with the venous 

 spaces surrounding the pulp-cords, so that finely divided substances, such as metallic 

 1 Johns Hopkins Hospital Bulletin, 1898 ; Zeitschrift f. Morphol. u. Anthropol., Bd. ii., 1900. 



