SURFACES. 



161 



liculus of the corpora quadrigemina, being continued directly 

 into the brachium inferius. Auditory conduction therefore 

 proceeds from the inferior colliculus through the brachium inferius 

 to the medial geniculate body and then through the acustic radi- 

 ation to the temporal cortex. Thus the lateral fillet forms the 



Fig. 48. Section of the mid-brain cutting the inferior cofliculi of the corpora 

 quadrigemina. (Original.) 



a. Sulcus lateralis. b. Fonnatio reticularis. c. Medial longitudinal bundle, d. Nucleus 

 of colliculus inferior, e. Aqueductus cerebri. f. Rubro-spinal tract, g. Lateral fillet, h. 

 Medial filliet. i. Basis pedunculi. j. Location of anterior longitudinal bundle, k. Interpedun- 

 cular fossa. 1. Substantia nigra. m. Decussation of brachia conjunctiva. 



second stage in the auditory conduction path. The acustic 

 nerve constitutes the first stage, the lateral fillet the second stage, 

 the brachium inferius the third, and the acustic radiation the 

 fourth stage. The last stage ends in the cortex of the superior 

 and the transverse temporal gyri. 



The spino-thalamic tract (Figs. 47 and 48) is located hi 

 the region of the nucleus lateralis superior. It is a loose strand 

 of fibers not isolated from surrounding structures; and, probably, 

 has many relays in its course. The spino-thalamic tract rises 

 in the gray substance of the spinal cord and in the terminal nuclei 

 of the common sensory cerebral nerves. Though it sends some 



