THE PONS VAROLII 255 



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 ob- 

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

 great commissure, for the reason that it contains white fibers con- 

 necting the two lateral halves of the cerebellum and the differ- 

 ent portions 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 longitudinal fibers are continuations upward 

 of fibers from the olivary 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 enceph- 

 alon above the pons does not deprive an animal of voluntary 

 motion and general sensibility. It will be seen later that the 

 integrity of the cerebrum is essential to any intellectual opera- 

 tion, and manifestly, under the conditions mentioned, there can 

 be no voluntary motion which indicates any degree of intelligence; 

 but the fact remains that the animal can perform movements 

 which are different from the reflex movements depending on the 

 presence of the cord when all other parts of the cerebro-spinal 

 axis have been removed. The pons is apparently "an organ 

 capable of originating impulses giving rise to voluntary move- 

 ments, when the cerebrum, corpora striata and optic thalami 

 have been removed, and it probably regulates the automatic 

 voluntary movements of station and progression." (Flint.) 



