THE PONS VAROLIJ 255 



nearest approach to instantaneous death, and the respiratory 

 center has, therefore, been called the "vital spot," though 

 death from any cause cannot be instantaneous. 



Some other reflex centers are for deglutition, sucking, se- 

 cretion of saliva, vomiting, coughing, sneezing, dilatation of 

 the pupil, secretion of sweat, secretion of glycogen, etc. 

 Typical of these is the reflex act of sneezing, in which case 

 impressions are conveyed to the medulla by the nasal 

 branches of the fifth nerve. 



Additional centers in the medulla are those which preside 

 over inhibition and acceleration of the heart, vaso-motor 

 centers for the vessel walls, and centers for special senses 

 like hearing and taste. There is also said to be here a center 

 controlling the production of heat by the tissues. 



The Pons Varolii. 



Anatomy. The pons is situated just above the medulla 

 oblongata at the base of the brain, and is frequently called 

 the great commissure, for the reason that it contains white 

 fibers connecting the two lateral halves of the cerebellum 

 and the different portons of the cord and medulla with the 

 parts of the brain above. It resembles the cord in having its 

 white matter situated externally, while within its substance 

 are a number of collections of gray matter. The longitudi- 

 nal fibers are continuations upward of fibers from the oli- 

 vary bodies and the anterior pyramids of the medulla and 

 also of parts of the posterior and lateral columns of the cord. 

 They pass through the crura cerebri to the brain. 



Functions. The anatomical structure and situation of the 

 pons at once suggest that its function is to transmit motor 

 impulses from and sensory impressions to the cerebrum. 



The gray centers, however, indicate a further function of 

 this organ. It is found that the removal of all parts of the 

 encephalon above the pons does not deprive an animal of 

 voluntary motion and general sensibility. It will be seen 



