1030 EVOLUTIONAL MODIFICATIONS 



In its progressive expansion, the inferior (jlivary nucleus is a distinctive 

 feature in the brain. Concerning the actual function of this important 

 structure, much Hght is still needed. The interpretation advanced in this 

 discussion of the primates, assigns to the nucleus an activity related to the 

 simultaneous coordination of the hand, liead and eye. Integration of widely 

 separated muscles so that they act as a single mechanism needs no argument 

 to defend its physiological necessity in the interest of highly organized motor 

 performances. A vast range of skilled acts depends upon the harmonious 

 action of the eye muscles in order to keep the objective m clear \ ision and 

 focus. The hands which perform the actual execution of the movements are 

 followed and directed by vision. The underlying motive for the simultaneous 

 cooperation in the muscles turning the eyes, turning the head, as well as 

 moving the hands and fingers, is thus ob\ ious. Ocular supervision is essential 

 both in the acquisition and the direction of a large number of skilled learned 

 performances. From the known facts concerning the mterior oli\e, this 

 nucleus stands as an intermediary between the ocular nuclei, lying above it in 

 the brain stem, and the nuclear centers forming the final common pathway 

 for motor impulses to the muscles of the neck and the upper extremities. 

 Equipped to receive proprioceptive impulses from the musculature ot the 

 eyeball, of the neck and of the upper extremity, the inferior olive is in a 

 position to transmit these incoming impressions to the cerebellum, not only 

 to its lateral lobes, but to some extent also to the vermis. It supplies in this 

 manner the afferent elements to the cerebellum necessary for the organiza- 

 tion of outgoing syntheses of coordinati\e impLilscs for all highly skilled 

 acts of the body. This is the control essential in the oculo-cephalo-gyric 

 movements utilized in the visual direction of many acts, such as handwriting, 

 painting, drawing and the employment of instruments and implements. 



Fundamentally the inferior oli\ e is an ancient structure. Those who have 

 given attention to its phyletic organization recognize in it at least two parts, 



