SUMMARY OF STRUCTURES 249 



mesencephalic nucleus of the trigeminal nerve. By some authorities this 

 latter nucleus is accredited with proprioceptive functions, receiving sensory 

 stimuli from the eye muscles. Some fibers of the central tegmental tract may 

 pass further cephalad in the direction of the basal ganglia of the endbrain 

 and also into the posterior commissure. The main bulk of this bundle seems 

 to terminate in the region of the nucleus oculomotorius. By means of it 

 connection is established between the chief nuclei concerned in regulation of 

 ocular movements and the inferior olive. A small and poorly myelinized tract 

 of fibers may be traced to the olive from origins in the cervical and upper 

 thoracic segments of the spinal cord. This is the spino-olivary tract of 

 Helweg. 



In the absence of other ascending or descending connections with this 

 important nuclear structure it seems probable that the olivary nucleus is an 

 intermediary station for impulses received from the muscles of the eye, neck, 

 upper extremity and perhaps the upper portion of the trunk. It ultimately 

 delivers these impulses to the cerebellum. Such connections might well serve 

 the purposes of simultaneous coordination in the ocular, neck, arm and 

 upper trunk muscles. The fact that experimental lesions of the inferior olive 

 disturb the coordmation of the eye muscles and cause pathological torsion in 

 the neck lends support to the theory that one of the functions of the olive, if 

 not its chief function, is simultaneous coordination of eye, head and hand 

 movements and also the performance of all highly skilled acts. This presump- 

 tion is borne out by the progressive increase in the conspicuity of the olive 

 while passing from the lowest of the primates to the highest members of this 

 order. 



OLIVARY SUBDIVISIONS 



Morphologically several olivary subdivisions have been recognized. 

 These include a portion which is old, often referred to as the paleo-olire, and 



