146 NORMAL HISTOLOGY. 



these cells we find spheroidal cells, like lymph-cells ; 

 large colorless cells with one or more large nuclei ; 

 red blood-cells ; fragments of red blood-cells ; larger 

 and smaller colorless cells containing pigment in 

 various forms. Finally, there are sometimes found 

 in varying number, cells which resemble the lymph- 

 and larger colorless cells in form, but whose bodies, 

 either homogeneous or granular, have a color sim- 

 ilar to that of the red-blood cells. These latter 

 cells, like certain similar cells already mentioned 

 as occurring in the marrow of bones, are called 

 nucleated red blood-cells, and are regarded by 

 many observers as intermediate forms between the 

 colorless and the red-blood cells. Although many 

 recent observations would tend to confirm this 

 idea, their nature is as yet by no means absolutely 

 determined. 



We have still to consider the structure of the 

 second constituent of the pulp the cavernous veins. 

 Following the splenic veins inward from the hilus, 

 we find that they gradually lose their connective- 

 tissue sheath, and then their outer coats, and then 

 rapidly divide and sub-divide to form a multitude of 

 intercommunicating thin-walled canals of tolerably 

 uniform calibre, which occupy the irregular-branch- 

 ing spaces between the pulp-cords. These ultimate 

 venous trunks are called cavernous veins, and their 

 walls consist of little else than a few widely separated, 

 branching, circular and oblique fibres, upon which 



