586 THE HUMAN BODY. 



tral organ of the nutritive processes. " The physiological 

 action of most of the medullary centres has already been 

 described; the more important are 1. The respiratory 

 centre (p. 390). 2. The cardio-inhibitory centre (p. 250); 

 (there is also some reason to believe that the centre of the 

 accelerator heart-fibres (p. 252) lies in the medulla). 3. 

 The vaso-motor centre (p. 253). 4. The centre for the 

 dilator muscle-fibres of the pupil (p. 486). 5. The centre 

 for the muscles of chewing and swallowing (p. 337), which 

 are commonly thrown into action reflexly, though they may 

 be made to contract voluntarily. 6. The convulsive centre 

 {p. 400). 7. The diabetic centre (p. 442). 8. The centre 

 reflexly exciting activity in the salivary glands, when sensory 

 nerves in the mouth are stimulated. 9. Certain centres 

 for complex bodily movements; an animal with its medulla 

 oblongata can execute much more complicated reflex acts 

 than one with its spinal cord alone. 



Functions of the Cerebellum, Pons Varolii, and Mid- 

 Brain. These contain paths of conduction between the 

 fore-brain and parts behind, and many important centres, 

 especially those concerned with the maintenance of the 

 equilibrium of the Body in various postures and modes of 

 locomotion. If, as has been above suggested, an animal 

 without its cerebral hemispheres has sensations which 

 remain untranslated into terms of external things, these 

 sensations must have their seats in these brain-regions. 



The crura cerebri (p. 164) are essentially paths of 

 conduction between the cerebral hemispheres and parts 

 behind. Injury of one produces partial loss of sensibility 

 and incomplete muscular paralysis on the opposite side of 

 the Body. The anterior pair of eminences of the corpora 

 quadrigemina are concerned with sight; stimuli reaching 

 them through the optic nerve, there, probably, first cause 

 visual sensations, which it is left to the fore-brain to interpret. 

 If the latter is removed from an animal light brought in 

 front of the eye still causes contraction of the pupil; direct 

 irritation of the eminences in question has the same effect, 

 and destruction of one of them causes blindness of the oppo- 

 site eye. The functions of the posterior pair of eminences 



