612 THE HUMAN BODY. 



than one nucleus and some of the nuclei are separated from 

 the gray matter around the central cavity, but a minute ana- 

 tomical description would be here out of place. The olivary 

 capsules, however, placed in the olivary bodies which lie on 

 the outer side of each anterior pyramid may, however, be 

 mentioned. The nerves having their nuclei in the medulla 

 oblongata are the hypoglossal (xn), the spinal accessory (xi) 

 except its spinal portion, the vagus (x), the glossopharyngeal 

 (ix) (some fibres of which perhaps come from the cord), the 

 auditory (vm) (by two distinct bundles of fibres, cochlear 

 and vestibular, connected with distinct nuclei), the facial 

 (vn), the patheticus (vi), part of the trigeminal. Some of 

 the trigeminal arises from gray matter in the corpora quad- 

 rigemina. The nucleus of the abducens (iv) lies just under 

 the floor of the aqueduct of Sylvius (Fig. 176), opposite the 

 posterior border of the anterior corpora quadrigemina. The 

 oculo-motor (in) arises from gray matter under the front 

 of the aqueduct and from the posterior part of the third ven- 

 tricle. All the fibres of the above ten nerves arise, then, 

 from gray matter around the cerebral continuation of the gray 

 matter of the cord, and most of them behind the midbrain. 



Besides its functions as affording paths between the cord 

 and the rest of the brain and as the seat of many relay and 

 junction centres the medulla has important reflex and auto- 

 matic activities. As in the case of the cord, its motor centres 

 may be thrown into reflex activity by afferent impulses from 

 below, as well as by efferent travelling down from cerebrum 

 or cerebellum. It is especially concerned with nervous con- 

 trol of the organs more immediately connected with circu- 

 lation, respiration, and mastication. The physiological action 

 of most of the medullary centres has already been described ; 

 the more important are 1. The respiratory centre. 2. The 

 cardio-inhibitory centre ; the centre of the accelerator heart- 

 fibres lies in the medulla. 3. The vaso-motor centres. 4. 

 The centre for the dilator muscle-fibres of the pupil. 5. 

 The centre for the muscles of chewing and swallowing, which 

 are commonly thrown into action reflexly, though they may 

 be made to contract voluntarily. 6. The convulsive centre. 

 7. The diabetic centre. 8. The centre reflexly exciting activ- 

 ity in the salivary glands, when sensory nerves in the mouth 

 are stimulated. 9. Certain centres for complex bodily move- 

 ments; an animal with its medulla oblongata can execute 



