THE CHIEF CENTER OP THE NERVOUS SYSTEM. 597 



or by communicating roots, but also where all nerves acquire 

 tlieir vasomotor properties. 



But what is the difference as regards the role of the nerv- 

 ous energy involved between a motor and a vasomotor nerve? 

 None, evidently, and perfect equipoise between the energy 

 transmitted to the cellular structures of an organ, and that 

 necessary for its vasomotor functions, being a sine qua non to 

 proper function, a single organ was intrusted by Nature with 

 the inciting and governing role: i.e., the posterior pituitary 

 body. Of course., this relegates all motor impulses "influenced, 

 arranged, and governed by coincident sensory or afferent im- 

 pulses" to this organ, and makes it the general center of the 

 motor system. We have previously referred to the fact that the 

 medulla is only a transmitting center: a general station to 

 which impulses from various directions arrive by the cord from 

 below, by the commissures from the encephalic structures, 

 and establish junctions with the several paths with which they 

 are related. "The encephalon is a very complicated system of 

 large and small continents of gray or central nervous sub- 

 stance," says Professor Duval, "communicating one with an- 

 other and with the medulla by numerous commissures." 



We have seen how absolutely independent of motor func- 

 tions the hemispheres are, though volitional attributes enable 

 them to utilize the motor system. Indeed, the experimental 

 evidence adduced on this score is incontrovertible. But the 

 same distinguished physiologist says: "The nerve-cells of the 

 cord form in this organ a continuous central gray mass, extend- 

 ing from one extremity of the organ to the other. But, if the 

 anatomist locates the superior limit of the cord on a level with 

 the occipito-atloidian articulation, for the physiologist the cord 

 extends into the interior of the cranium; it reaches to the 

 aqueduct of Sylvius (the true origin of the motor oculi com- 

 munis and patheticus) and even on a level with the third ven- 

 tricle the gray substance of the walls of this ventricle." We 

 have seen that he also referred to its reaching up to the sella 

 turcica. That it is within this bony structure that the main 

 center of this vast mechanism with its extensions and ter- 

 minals, including the vasomotor fibers lies we have suffi- 

 ciently emphasized. We feel, therefore, that we have good 



