INTERNAL STRUCTURE OF THE BRAIN STEM 1031 



i. c, the palco-olive and the nco-olivc. In the lower forms of animals not yet 

 possessed of anything approaching manual differentiation, the need of an 

 intimate cooperation betw een muscles of the eyes, of the neck and of the 

 upper extremity is not pronounced. These animals in consequence depend 

 upon the associations of a much simpler range of motion. To them the coor- 

 dination of the neck muscles controlling the movements of the head, and of 

 the eye muscles regulating the mo\ements of the eyeballs, may be essential 

 in such acts as browsing or grazing, particularly to animals possessing long 

 necks, such as the giraffes. These species arc not in need of simultaneous 

 coordination in the ocular, cer\ical and brachial muscles. In consequence, 

 although they have developed an inferior olnarv nucleus, this structure 

 appears in its simplest form. It consists largely of what is properly called 

 the palco-olive. The paleo-olivary connections with the cerebellum are for 

 the most part w ith the central portion or vermis. In animals possessing claws, 

 such as those of the canine and feline families, there is at least some slight 

 demand for coordinative action between the muscles of the eye, neck and 

 upper extremities. In such species the inferior oli^ ary nucleus shows consider- 

 able advance notwithstanding the fact that it still remains, from a structural 

 standpoint, in a fairly primitive condition. Canine and feline activities in 

 which the claws are employed, as in digging holes for burying food, require a 

 certain degree of mutual coordination in oculo-cephalo-gyric and upper 

 extremity mo\ements. These mo\ ements unquestionably belong to the cate- 

 gory of performances learned by imitation. In consecjuence there is some 

 increase in these animals of the inferior olive and the olivo-ccrcbellar 

 connections. 



W hh the advent of the primates, manual differentiation became a 

 feature of progressive development. The influence of this new impulse was 

 immediately impressed upon the inferior olivary body. Even in the lemurs, 

 the nucleus manifests tendencies toward expansion in its neo-olivary portion 



