5 g TEXT-BOOK OF PHYSIOLOGY 



of the face, this power being lost in certain pathologic conditions. The 

 power of regulating the temperature of the body has been also assigned to 

 the thalamus, as destruction of its anterior extremity is usually followed by 

 a rise in temperature. 



The Internal Capsule. The internal capsule has been shown by the 

 results both of experiment and of pathologic processes to be, first, a pathway 

 for the transmission of nerve impulses from the cerebral cortex to the pons, 

 medulla, and spinal cord, which give rise to contraction of the muscles of the 

 opposite side of the body; and, second, a pathway for the transmission of 

 nerve impulses coming from skin, mucous membrane, muscles, and special 

 sense-organs to the cortex, where they give rise to sensations general and 

 special. It is therefore the common motor and sensor pathway. For the 



FIG. 240. HORIZONTAL SECTION OF THE INTERNAL CAPSULE SHOWING THE POSITION AND 

 RELATION OP THE MOTOR TRACTS FOR THE EYE, HEAD, TONGUE, MOUTH, SHOULDER (Shi.), 

 ELBOW (Elb.), DIGITS OF HAND (Die.), ABDOMEN (Abd.), HIP, KNEE (Kn.), DIGITS OF FOOT 

 (Dig.). S. Sensor tract. O. T. Optic tract. A. T. Auditory tract. 



reason that it transmits both motor and sensor impulses, and for the further 

 reason that it is frequently the seat of pathologic lesions which are followed 

 by either a loss of motion or sensation or both, the internal capsule is one 

 of the most interesting parts of the central nerve system. As shown in Fig. 

 243, it consists of two segments or limbs united at an obtuse angle, the knee 

 or elbow, which is directed toward the median line. The motor tract is 

 confined to the posterior one-third of the anterior segment and the anterior 

 two-thirds of the posterior segment. The sensor tract is confined to the 

 posterior one-third of the posterior segment, the extreme end of which also 

 contains the optic and auditory tracts. 



The region of the anterior segment in front of the motor tract contains 

 the fibers of the fronto-cerebellar tract, the function of which is unknown. 



The motor region contains fibers which descend from the cerebral cortex 



