THE MEDULLA. 



95 



the Accessorius (Fig. 43): a nerve which left the same cell-column farther 

 posterior; also a part of the motor vagus root (Fig. 46) presents a similar 

 thing. "We now come to the two nerves which arise from the major part of 

 the cell-column under consideration: viz., the Facialis and the motor 

 Trigeminus. Both are not always sharply difEerentiated from each other in 

 the region of the roots. In the lower vertebrates the motor Facialis is 

 usually much smaller than the masseteric branch of the Trigeminus, prob- 

 ably because the face-musculature is less developed. Fig. 49 shows the posi- 

 tion of the Facialis and of the nucleus of the Abducens in the alligator and 

 in Fig. 50 is presented a section which cuts the motor column at a higher 

 level when it dilates in the dorsal portion for the nucleus of the Trigeminus. 

 The nucleus of the Facialis is not a single structure. In the longitudinal 

 as well as in the antero-posterior direction it shows interruptions. For 



Fig. 51. — Lacerta agilis. Region of exit of the Trigeminus (N.T.). 



that reason one might easily designate in different animals different cell- 

 groups as the origin of the nerve. But all of these cell-groups belong to the 

 same mass of great multipolar cells, whose neuraxons pass into motor nerves. 

 At the anterior end of the medulla the gray mass which received the 

 sensory nerves on the latero-dorsal aspect becomes again very much en- 

 larged. At this point the Trigeminus nerve enters it. In this frontal 

 sensory nucleus of this nerve only a part of the fibers from the Gasserian 

 Ganglion end, while a greater part turn toward the spinal cord, there to 

 gradually enter the gray matter, which we see in all sections from the upper 

 end of the spinal cord to the entrance of the Trigeminus into the medulla. 

 This descending portion has been described as the bulbospinal root of the 

 Trigeminus. In such aquatic animals as fishes, dipnoi, and larval amphibia 

 there exists over the whole head a system of canals bearing a sensory epithe- 

 lium: an apparatus which probably serves for the detection of changes of 



