FUNCTIONAL ANALYSIS, CENTRAL AND PERIPHERAL (»3 



after transection immediately below the auditory vesicle under con- 

 trol of the lower medulla oblongata and spinal cord (Coghill, '26, 

 Paper VI, p. Ill; '29, p. 15); but, subsequent to Harrison's stage 40, 

 Detwiler finds that sustained motor activities, including swimming, 

 fail rapidly if the influence of the midbrain is blocked in prefunc- 

 tional stages, though feeding reactions are preserved after complete 

 ablation of hemispheres and visual organs. The midbrain evidently 

 supplies a factor essential for maintenance of motor efficiency. 



The motor field of this brain is smaller and more simply organized 

 than the sensory field because most of the activities are mass move- 

 ments of total-pattern type. Within this larger frame of total be- 

 havior, the partial patterns of local reflexes are individuated with 

 more or less capacity for autonomous action. The number of these 

 local partial patterns is smaller than in higher animals, and all of 

 them are far more closelj^ bound to the total patterns of which they 

 are parts. The segments of each limb, for instance, may, upon ap- 

 propriate stimulation, move independently; but in ordinary locomo- 

 tion they move in a sequence related to the action of the entire limb, 

 the other limbs, and the musculature of the trunk. 



The peripheral motor nerves (omitting the general visceral com- 

 ponents of preganglionic type not here considered) are in three 

 groups: (1) the spinal nerves; (2) the eye-muscle nerves. III, IV, and 

 VI pairs of cranial nerves, which are somatic motor; and (3) the 

 special visceral motor nerves of the V, VII, IX, and X pairs, in- 

 nervating the striated musculature of the visceral skeleton of the 

 head. The primary movements of trunk and limbs are organized for 

 locomotion in the motor zone of the spinal cord. This organization is 

 under exteroceptive and proprioceptive control locally throughout the 

 length of the cord and more especial!}^ at the bulbo-spinal junction; 

 it is under additional proprioceptive control from the labyrinth and 

 the cerebellum; there is further control from the cerebrum — optic, 

 olfactory, and the related apparatus of higher correlation. The bulbar 

 group of special visceral motor nerves is primarily concerned with 

 movements of the head, notably those of respiration and feeding. 

 The feeding reactions are under visual, olfactory, somesthetic, gusta- 

 tory, and general visceral afferent control, and the pattern of per- 

 formance seems to be organized in the large isthmic tegmentum. 

 The very large and complicated interpeduncular nucleus is an isthmic 

 structure which is physiologically of intermediate-zone type (chap. 

 xiv) . Details of the structure and connections of the various parts of 



