INTERLACEMENT OF THE CEREBELLAR BRACHIA. 4)53 



fore the loop layers) between the posterior longitudinal fasci- 

 culi and the red nucleus of the tegmentum, and partly exter- 

 nally to the latter. The first-named tract then obviously 

 passes across the middle line, and, investing the inferior peri- 

 phery of the red nucleus, may be followed far outwards. Both 

 on the proximal and on the distal side of the decussation, in 

 the adult, there are distributed amongst these fibrce arcuatce, 

 proceeding from the column of the fifth nerve, pigmented nerve 

 corpuscles, having a length of 60 /x, and a breadth of 15 ju, the 

 processes of which form a communication between the origins 

 of the motor columns of the spinal cord and the arcuate fasci- 

 culi of the strands of the fifth nerve. 



A retrospective glance at the organization f the tegmentum 

 shows that two fundamental differences exist in the structure 

 of its ganglia as compared with the erusta, which are adapted 

 to assist us in determining the significance of these two tracts 

 of origin of the spinal cord. 



In the first place, the tegmentum is characterized by the con- 

 currence, on the one hand, of the tractus opticus, and of the origin 

 of (motor) columns of the spinal cord in its grey masses, as well 

 as, upon the other hand, by the communication of the strands 

 of the fifth pair of nerves with these columns through the 

 intermediation of multipolar nerve cells, forming a territory of 

 reflection of centripetal excitation into motion. The ganglia 

 of the erusta, on the ether hand, having no connection with 

 sensorial peripherie expansions, point to another source for the 

 excitation of their motor powers; namely, to the conditions of 

 excitation of the cerebral lobes. 



In the second place, the nuclei of origin of the tegmentum 

 are centres in which the anatomical arraagement constitutes a 

 mechanism for the production of certain combined movements 

 which can be called into action by the just-mentioned centri- 

 petal impulses. This characteristic they obtain from the differ- 

 ent origins of the columns of the spinal cord in these ganglia, 

 and especially from their partly decussating and partly non- 

 decussating mode of origin from one and the same ganglion 

 (optic thalamus). As a consequence of this, we may expect 

 that the innervation affecting the ganglion of one side may 

 bring unsymmetrical muscles of the two halves of the body 



