THE SPLEEN. 409 



branches from them subdivide, pass into the pulp, and end in 

 the venous radicles we have described. 



It is proper to state that some authors (Gray, Billroth, 

 Kolliker) believe that the capillaries connect directly with 

 these cavernous veins, pouring the blood into the lacunae which 

 they form. Others (Key, Stieda) believe that the sustenacular 

 tissue of the pulp is not composed of branching fibrillse, but 

 of collapsed capillaries, which connect the arteries with the 

 venous radicles. Such views cannot now be sustained. 



The lymphatics of the spleen occur in two sets : one, the 

 trabecular, forms a close plexus in the external capsule and 

 sends deep branches along the trabeculse, to communicate with 

 the deep or perivascular set. This perivascular set arises from 

 the lymphoid sheaths of the arteries, and at first has no dis- 

 tinct channels. True lymphatics are soon formed, however, 

 which run along the arteries, generally one on each side. At 

 the hilum they unite with the trabecular set, and, passing along 

 the gastro-splenic omentum, enter the neighboring lymphatic 

 glands. 



The nerves are derived from the solar plexus (right and left 

 semilunar ganglia and right pneumogastric). They enter the 

 hilum and follow the course of the arteries ; along their terminal 

 ramifications, according to Miiller, are oval ganglia, through 

 which a single fine capillary runs. On section of the nerves of 

 the spleen the organ dilates, and on electrical stimulation it 

 contracts. 



Development. The spleen is present in all vertebrates ex- 

 cept the septocardia and myxenoids (Miiller). 



The organ is developed entirely from the mesoblast, and, 

 according to Peremeschko, is intimately related in its origin 

 with the pancreas, from which it is an offshoot. Its shape can 

 be recognized in the twelfth week. The capsule, trabecuhe, and 

 retiform connective tissue, are first formed ; then the cells and 

 Malpighian bodies appear, the latter at about the middle of 

 intra-uterine life. 



Preparation of spleen for microscopical examination. 

 The methods of preparing the spleen for examination are in 

 general like those for preparing lymphoid tissue anywhere. 

 The organ is very soft, and the object to be aimed at is to 

 harden it without interfering too much with its intimate struc- 

 ture. A good method is that of Klein. The spleen should be 



