FUNCTIONS OF THE MEDULLA AND ISTHMUS 565 



roots of the first and second dorsal nerves and reaching the heart through 

 the sympathetic nerve; (2) an inhibitor or retarding action on the rate 

 of the heart-beat through efferent fibers in the trunk of the pneumogastric 

 or vagus nerve. (See pages 322 and 323.) 



A vaso-motor center, which regulates the caliber of the blood-vessels 

 throughout the body in accordance with the needs of the organs and 

 tissues for blood, through nerve-fibers passing by way of the spinal 

 nerves to the walls of the blood-vessels. (See page 382.) 



3. A respiratory center, which coordinates the muscles concerned in the 



production of the respiratory movements. (See page 425.) 



4. A mastication center, which excites to activity and coordinates the muscles 



of mastication. (See page 144.) 



5. A deglutition center, which excites and coordinates the muscles concerned 



in the transference of the food from the mouth to the stomach. (See 

 page 164.) 



6. An articulation center, which coordinates the muscles necessary to the 



production of articulate speech. 



^ A diabetic center stimulation of which gives rise to glycosuria. 

 8. A salivary center, stimulation of which excites the discharge of saliva. 



B. The Medulla and Isthmus as Conductors. The anterior pyra- 

 mids of the medulla and their continuations through the more ventral por- 

 tions of the pons, being portions of the general pyramidal tract, serve to 

 conduct volitional efferent nerve impulses from higher portions of the brain 

 to the spinal cord. Division of these pathways is at once followed by a loss 

 of volitional control of the muscles below the section. 



The dorsal or tegmental portion, containing the fillet, serves to transmit 

 afferent nerve impulses from the spinal cord to higher portions of the brain. 

 Transverse division of one-half of the dorsal portion of the pons is followed 

 by complete anesthesia of the opposite half of the body without any im- 

 pairment of motion. 



The restiform bodies constitute a pathway between the spinal cord and 

 the cerebellum. The transverse fibers of the pons associate opposite but 

 corresponding portions of the cerebellar hemispheres. 



The crura cerebri consists ventrally of fibers which are largely derived 

 from the pyramidal tracts and are continuous with the longitudinal fibers 

 of the ventral portion of the pons and medulla; and dor sally of fibers continu- 

 ous with those coming through the lower portions of the tegmentum. Hence 

 they are conductors of motor impulses in the former and of sensor impulses 

 in the latter region. It is not definitely known as to whether reflex actions 

 take place through the gray matter, the locus niger, or not. 



The Corpora Quadrigemina. From the anatomic relation of the 

 superior quadrigeminal body (the pre-geminum) to the optic tract, the 

 inference can be drawn that it is in some way essential to the performance 

 of various reflex ocular movements and perhaps to the variations in size of 

 the pupil. Experimental investigations and pathologic changes support the 



inference. 



Irritation of the pre-geminum in monkeys on one side is followed by 

 diminution of the pupils first on the opposite side and then almost immedi- 

 ately on the same side. The eyes at the same time are also widely opened and 

 the eyeballs turned upward and to the opposite side. If the irritation be 



