Wide vessels in the spleen that drain into trabecular veins[WP].
Comment:
[taxon-note] "Whereas man and the rat are in the 'sinusal' group, the mouse belongs in the 'nonsinusal' group. The red pulp of spleens of rat, dog, man, and many other mammals contains an elaborate plexus of sinuses; that of mouse, cat, pig and others has no true sinuses and relatively few veins leading from the meshes into collecting veins - http://www.informatics.jax.org/greenbook/chapters/chapter13.shtml"