212 HUMAN PHYSIOLOGY. 



ter ; the posterior portion governs the opening and shutting of the 

 mouth and the protrusion and retraction of the tongue. 



2. The upper limb area may be subdivided as follows : The upper 

 part controls the movements of the shoulder ; posteriorly and be- 

 low this point are centers for the elbow ; below and anteriorly, 

 centers for the wrist and finger movements, while lowest and pos- 

 teriorly, centers governing the thumb. 



3. The leg area may be subdivided as follows : The anterior part, 

 both on the mesial and lateral surfaces, contains centers governing 

 the hip and thigh movements ; in the posterior part are centers 

 for the movements of the leg and toes. The center for the great 

 toe has been located in the paracentral lobule. 



4. The trunk area, situated largely on the mesial surface, contains 

 anteriorly centers governing the rotation and arching of the 

 spine, while posteriorly are found centers governing movements of 

 the tail and pelvis. 



5. The head area, or area for visual direction, contains centers ex- 

 citation of which causes " opening of the eyes, dilatation of the 

 pupils, and turning of the head to the opposite side, with conju- 

 gate deviation of the eyes to that side." 



The centers of origin of the nerves for the ocular muscles lie in 

 the gray matter of the aqueduct of Sylvius. Destruction of the 

 gray matter at these points is followed by paralysis of the muscles 

 of the opposite side of the body, and morbid growths, hemorrhages, 

 or thrombi of the vessels of the part result in abnormal stimulation 

 or in interference with the functions corresponding to the nature 

 and extent of the lesion. Cerebral or Jacksonian epilepsy is a 

 result of local cortical disease. 



Center for Speech. Pathologic investigations have demonstrated 

 that the left third frontal convolution is of essential importance for 

 speech. Adjoining this convolution are the centers controlling the 

 motility of the lips, tongue, etc. In the majority of cases the speech 

 centers are on the left side of the brain, though in exceptional 

 cases they are on the right side, especially in left-handed persons. 

 In deaf mutes this convolution is very imperfectly developed, while 

 in monkeys it is quite rudimentary. 



Lesions of the third frontal convolution on the left side, if the 

 patient be right-handed, produce the various forms of aphasia, or 

 the partial or complete loss of the power of articulate speech. 



