Page:Popular Science Monthly Volume 26.djvu/764

 the functions of the pons Varolii. Section or irritation of this organ is followed by powerful movements, and much more pronounced signs of pain than any previously manifested. If we cut the anterior portion of one side of the pons, movements will be produced on the opposite side of the body, and the vertebral column will bend toward the side of section. It has been shown that the deeper posterior parts of the pons are made up of transverse fibers connecting the two lobes of the cerebellum, and we find, as we should expect, that injury to one side of this portion of the organ causes the same rolling movements as appear upon one-sided injury to the cerebellum.

If we remove all the encephalic centers above the pons, the animal so treated will maintain his upright position, will give cries quite characteristic of pain, and will bring about conjoined movements of flight. These manifestations disappear completely after removal of the pons, and we have left only those reflex activities already shown to be dependent

 showing the inner face of Left Cerebral Hemisphere. (Sappey, after Hirschfeld.) 1. spinal cord; 2, pons Varolii; 3, cerebral peduncle; 4. "arbor vitæ;" of cut surface of middle lobe of cerebellum; 5, Svlvian aqueduct; 6, valve of Vieussens; 7, corpora quadrigemina; 8, pineal body: 9, its inferior peduncle; 10, its superior peduncle; 11, middle portion of the great cerebral cleft; 12, upper face of the thalamus; 13, its internal face, forming one of the walls of the middle or third ventricle.

upon the cord and medulla. It seems clear that in the cell-masses of the pons the movements essential for locomotion, for maintenance of upright position, and for expression of pain, are combined. These phenomena have led many physiologists, among them Longet, to consider the pons as a sensorium commune, or the place where the sensations are assembled, and where the movements caused by sensations arise. Other physiologists, among them J. Müller, believe that the pons is the seat of the power of volition. I would reserve my opinion as to the relation between this organ and consciousness until after the functions of other nerve-masses between the pons and cerebral hemispheres have been considered.