570 THE CORPUS RESTIFORME. 



The corpus restiforme, is continuous with the posterior column 

 of the cord, enlarges as it ascends, and gradually recedes from 

 its fellow of the opposite side, and turns backwards and out- 

 wards, to throw itself into the cerebellum, of which it forms the 

 inferior part of the crus, e fig. 224. The cavity left by this 

 divergence seen only on the upper part of the medulla oblongata, 

 forms a part of the fourth ventricle, (sinus quadratus,) and is in 

 its shape resembling the letter V ; the posterior median fissure 

 extended through it, gives it the appearance of the nib of a pen, 

 and it was therefore called the calamus scriptorius, by Herophi- 

 lus. Part of the lateral portion called innominata, goes upwards 

 towards the cerebrum, and part may be traced backwards, ter- 

 minating insensibly on the sides of the corpus restiforme, and 

 going with it to the cerebellum. By cutting off the corpus res- 

 tiforme at the crus of the cerebellum, and stripping it downwards, 

 we separate the column of sensation from that of motion ; the 

 cavity of the fourth ventricle is then found expanded, and a mass 

 of cineritious substance is seen exposed at top of the calamus 

 called tuberculum cinereum, or fasciola cinerea by Wenzel, which 

 is continuous below, with the posterior horn of cineritious sub- 

 stance in the cord, and upon the sides with the corpus restiforme ; 

 the gray substance of which, is here increased in bulk exactly in 

 proportion with the increase of the corpus restiforme over the 

 posterior column of the cord. 



The antero-lateral column of the spinal marrow is continued 

 up over the anterior and lateral surface of the medulla oblon- 

 gata to the pons varolii, constantly increasing in size, and upon 

 it are developed the corpus pyramidale and corpus olivare ; a 

 part of its fibres though, as just observed, passing off towards 

 the cerebellum. Fifteen to eighteen lines below the pons varolii, 

 is seen in the anterior median fissure after the removal of the 

 pia mater which dips into it, a decussation of white fibres which 

 nearly obliterates the fissure, fig. 224. This crossing, is tech- 

 nically called the decussation of the pyramids, and is formed 

 of three or four bands of medullary matter which pass over 

 from each anterior column to the opposite side, then run 

 upwards parallel with the median fissure, and constitute the 



