Alcoholic Injection in the Mid-brain of the Cat 105 



cent, alcohol injected into the nucleus ruber with a fine hypoder- 

 mic syringe. The needle should enter the surface at about the mid- 

 dle of the colliculus and be directed slightly medially and at right 

 angles to the long axis of the brain stem to a depth of 1 cm. 

 After the usual two weeks, the animal was killed and the brain 

 carried through the regular Marchi method. 



As the accompanying illustrations show, it is possible in this 

 manner to cause degeneration of the entire extent of four de- 

 scending tracts, two of which are not easily recognizable on 

 normal material and yet are functionally of great importance. 

 These fiber bundles in the cat are situated in the same relative 

 position as in man. 



Although the exact course (especially peripherally) of the 

 mesencephalic root of the trigeminal nerve has been much de- 

 bated 2 , it is clearly evident that its exit through the pons is closely 

 associated with the motor root of the trigeminal nerve. 



The fibers from the nucleus of the medial longitudinal fascicu- 

 lus (degenerated only on one side) and those from the tectum 

 mesencephali (degenerated mostly on the contralateral side) oc- 

 cupy distinct regions throughout their entire course in the cat. 

 Numerous other experiments in which we have limited the lesion 

 to the tectum of the mid-brain have failed to show that any fibers 

 from this region enter what is strictly the medial longitudinal 

 fasciculus. The lower termination of the tectospinal fasciculus 

 has been variously given 3 . In this and the other experiments 

 referred to above, fibers of this fasciculus cannot be followed 

 farther than the upper part of the 7th cervical segment. It is 

 very probable that the fibers followed below this level by others 

 belong to some other tract such as the medial longitudinal fascicu- 

 lus, which extends throughout most of the spinal cord. It is the 

 large number of ascending and descending fibers from the vesti- 

 bular nuclei that make it appear that the medial longitudinal 

 fasciculus is partly mixed with the tectospinal. A clearer desig- 

 nation of the various fiber tracts now generally considered as 

 part of the medial longitudinal fasciculus is highly desirable. 



2 Allen, W. F., Jour. Comp. Xeur., 1919, xxx, 169. 

 s Collier, J. and Buzzard, F., Brain, 1901, xxiv, 177. 



