376 T^i'KNAi. OF Comparative Neurology. 



nucleus, within which is a large, densely stained granular 

 nucleolus. 



TRACTS OF THE METENCEPHALOX. 



Root of the Trigeminal Nerve. — In the amphiban brain, 

 according to Professor Osborn,(') the fifth nerve root is com- 

 posed of the following tracts: i. Ascending tract of the 

 cervical region, reinforced by 2, fibres from the deep motor 

 nidulus, representing two tracts. 3. Fibres from the sensory 

 nidulus. 4. Descending tract from the mesencephalic nidulus. 

 4. Direct encephalic tract. 



In the avian brain the composition of the root of the tri- 

 geminal nerve tallies even more closely with the composition 

 of the corresponding nerve of the human metencephalon.(-) 

 As in the human brain, so here this nerve is composed of two 

 distinct roots, each of which is composed of several distinct 

 fasciculi. In the lower types of birds ( Columba livia, etc.) 

 this appearance is quite distinct, but in the higher types 

 {^Hylocichla sxvainsoni , etc.) it is often somewhat obscured. 

 One of these roots lies caudad to the other. The cephalad 

 root is composed of two fasciculi, the lateral motor fasciculus 

 and the ascending cervical fasciculus. The caudad root is 

 also composed of two tracts, the lateral sensory fasciculus 

 and the deep motor fasciculus. 



Lateral Motor Fasciculus of the Trigeminal Nerve (Plate 

 XVIII, Fig. 8). This is a short bundle of loosely aggregated 

 fibres which passes from the lateral motor nidulus of the tri- 

 geminal nerve laterad into that nerve. This tract is feebly 

 convex, the convexity projecting caudad. 



Ascending Cervical Fasciculus of the Trigeminal Nerve 

 (Plate XVIII, Fig. 16). — This is a narrow fasciculus, which, 

 after passing entad for a short distance, turns abruptly and 

 passes caudad into the myelon. 



Lateral Sensory Fasciculus of the Trigeminal Nerve 



I " Amphibian Brain Studies," Jour, of Morphology, Vol. II, p. 69. 

 a See Rannev's " Applied Anatomy of the Nervous System," p. 338. 



