FUNCTIONS OF THE CRURA CEREBRI. 533 



The Medulla Oblongata and Pons as Centers for Reflex Activities: 



Experimentation has shown that the medulla and pons contain a number 

 of such centers, the more important of which are as follows: 



1. Cardiac centers, which exert (i) an accelerator action over the heart's 



pulsations through nerve-fibers emerging from the spinal cord in the 

 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 313, 314.) 



2. 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 372.) 



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



production of the respiratory movements. (See page 416.) 



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



of mastication. (See page 142.) 



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 162.) 



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



production of articulate speech. 



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



In addition, the gray matter contains centers which influence the secretion 

 of saliva, provoke vomiting, coordinate the muscles of the face concerned in 

 expression, and control the secretion of the perspiration. 



As Conducting Pathways. The anterior pyramids of the medulla and 

 their continuations through the more ventral portions 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. Divi- 

 sion 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. 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 dorsally of fibers continuous with those coming through the lower por- 

 tions 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 gray matter beneath the aqueduct of Sylvius contains nerve-cell 



