DEVELOPMENT OF THE MAMMALIAN SPLEEN 297 



3. Arterial capsules 



A study of the differentiation that accompanies the develop- 

 ment of the arteries leads one to the questions concerning the 

 splenic capsules or 'Hiilsenarterien' as first described by Schweig- 

 ger-Seidel. This observer found the capsules present in both the 

 human and pig spleens. In the human spleen no sharp line of 

 demarcation was seen between the capsule and the reticulum, but 

 in pig the two were distinctly separated from each other. The 

 adventitia was reported as being continuous with the capsule, 

 and the whole structure was thought to serve as a filter. 



Miiller saw a thickening in the adventitia of the arteries of the 

 human spleen which he thought was similar to the capsules of 

 other forms. He considered them as endings for nerve fibers. 



Kyber doubted the communication of the spaces in the capsule 

 with the lumen of the artery, believing that they connect with 

 the lymph system and are filled with lymphoid cells. 



Bannwarth, in studying the spleen of cat, found that the spaces 

 of the capsule that are not lined by endothelium serve as chan- 

 nels for the passage of cellular elements from the capsule to the 

 parenchyme of the organ. He adds that the capsules and the 

 endothelium are derived from a common 'Keim- oder Grundge- 

 webe' during their development, and that the later differentiation 

 of this tissue is dependent upon the amount available. If the 

 amount of this tissue is small, an ordinary capillary is developed, 

 but if there is an abundance present a capsule is formed. Dur- 

 ing embryonic life the latter serve as forerunners of the follicles, 

 but in later life they are buds of growth for tissue that enters the 

 splenic pulp. 



Kultschitzky is of the opinion that the cells of the capsules 

 are leucocytes. 



Whiting sees more of the details of the structures and reports 

 that blood cells pass between the muscle cells into the tissue of 

 the capsule and from there into the sinus that surrounds it. 



Weidenreich gives considerable attention to the 'Htilsen' of the 

 himaan spleen. Here they are characterized by a gradual increase 

 in the size of the wall of the artery which disappears gradually on 

 the opposite end, thus giving the capsule the shape of a spindle. 



