10 Journal of Comparative Neurology. 



between IX and VIII. Both reappear just behind the root of 

 VIII ; the ventral continues for about one-half millimeter in the 

 region of the VII-VIII root complex (Fig. 1 1), and the lateral 

 continues forward to the root of VI at the isthmus. This ceph- 

 alic part of the lateral column forms a large projection into the 

 .ventricle. 



The cells in both columns are usually spindle-shaped, 

 closely set, and the dendrites have long branches spreading 

 widely in the fiber tracts. The cells in the cephalic part of the 

 lateral column are so numerous that they are crowded into a 

 radial arrangement (Fig. 1 1 a). The cell bodies are much elon- 

 gated and distinctly spindle-shaped ; th^y converge toward the 

 outer part of the column, which lies near the spinal V tract, 

 and diverge toward its internal convex border. The inner ends 

 of the cells give off many small dendrites which form a fiber 

 zone of considerable thickness between the motor cells and the 

 ependyma. Larger dendrites from the outer ends of the cells 

 penetrate the lateral tracts. The spaces between the cell bodies 

 seem to be entirely free from fibers. 



The mode of origin of the motor nerve roots is as follows. 

 The large hypoglossus arises by several rootlets in cephalo- 

 caudal succe^sion, the fibers coming from the cells of the ventral 

 motor column of the same side (Fig. 6). 



The roots of X, both sensory and motor, are so small that 

 it is impossible to make out their central relations without the 

 aid of GoLGi sections. The motor roots can be traced in haema- 

 toxylin sections and it is apparently these which Ahlborn ('84) 

 has described under the name of the " vier hinteren sensiblen 

 Vaguswurzeln. " The root described by him as the motor vagus 

 is a part of the hypoglossus. The "vier hinteren sensiblen 

 Vaguswurzeln" arise according to Ahlborn from the " obere 

 laterale Ganglion" of Langerhans, i. e., from the group of 

 cells described above as the lateral motor column. Four such 

 rootlets are found in Lampetra and, as Golgi sections show, at 

 their point of exit from the medulla they contain both sensory 

 and motor fibers intricately interwoven. The sensory fibers run 

 on to the dorsal median portion of the medulla (Fig. 8). They 



