STRUCTURE AND FUNCTIONS OF THE CEREBRUM 145 



are the head senses whose central connections are best known. 

 The central connections of the sense of smell are imperfectly 

 known; those of taste practically not at all. Axons conveying 

 visual impulses enter the midbrain by way of the optic nerves 

 and optic tracts and terminate for the most part in nuclei of the 



Entering posterior 

 root 



Lissauer's tract 



' Emerging anterior root 



FIG. 66. Diagrammatic transverse, section of the spinal cord showing the con- 

 duction paths. (Cunningham.) 



midbrain, the external geniculates and superior colliculi; some 

 of them appear to terminate in basal nuclei of the cerebrum, the 

 optic thalami. In all these nuclei synaptic connection is made 

 with new neurons which carry the impulses into the cerebrum. 



Auditory impulses enter the medulla by way of the auditory 

 nerves. The axons of the nerves themselves terminate in nuclei 

 of the medulla, the auditory nuclei; new neurons continue the 

 path thence across the mid-line of the medulla and forward into 

 the midbrain, terminating in the internal geniculate nuclei and 

 the inferior colliculi. From these nuclei a third set of neurons 

 continue the path to the cerebrum. 



General Structure of the Cerebrum. This organ consists, as 

 previously stated, of an outer surface of gray matter, two milli- 

 meters thick, overlying a mass of white matter; the whole held 

 together by neuroglia and connective tissue, and mounted upon 



