THE CEREBRUM 



597 



Gushing has recently recorded the results of stimulation with the electrical 

 current of the post-central convolution in two conscious patients. The local- 

 ized stimulus gave rise to definite sensations which were likened in one 

 case to a sensation of numbness, and in the other to a definite tactual im- 

 pression. From the foregoing facts it may be stated in a general way that 

 the post-central convolution is the region for tactile (light touch) and asso- 

 ciated forms of sensation such as tactile discrimination and localization and 

 perhaps of the finer shades of temperature, in other words of epi-critic 

 sensibility. 



2. The Muscle Sense Area. The area of muscle sensibility has been assigned 



to the region posterior to but adjoining the post-central convolution and 

 includes the anterior part of the super-parietal and the supra-marginal 

 convolution on the lateral aspect and a portion of the callosal convo- 

 lution on the mesial aspect of the hemicerebrum. 



The sensations which are evoked in response to the action of nerve 

 impulses coming from tendons, muscles, etc., are those of passive position 

 and the direction and duration of movements of parts of the body. Clinic 

 observations and post-mortem findings indicate that lesions of this area are 

 followed by a loss of the muscle sense. Owing to the close juxtaposition 

 of the areas of cutaneous and muscle sensibility it is unusual to find a loss 

 of muscle sense without impairment of the tactile sense, not infrequently 

 they coexist. Surgical removal of a small angioma posterior to the post- 

 central convolution and about the junction of the super- and sub-parietal 

 convolutions was followed by a loss of the muscle sense in the opposite hand 

 and forearm without any disturbance of other sensations (Starr and McCosh). 

 In addition to sensations of passive position and direction of movements, 

 the sensations of temperature and deep pressure are also associated with 

 the physiologic activities of this region of the parietal lobe. There is much 

 obscurity as to the location, however, of the area in which sensations of pain 

 are evoked. These two areas together constitute the area of the body-feelings 

 or the somaesthetic area. 



Subdivisions of the Cutaneous and Muscle Sense Areas. Clinic observa- 

 tions and post-mortem findings also warrant the deduction that the general 

 areas of cutaneous and muscle sensibility are physiologically subdivided 

 as is the general motor area (see page 590) into areas for the skin and 

 muscles of the face, arm, trunk, and leg which occupy respectively areas 

 that adjoin the corresponding subdivisions of the motor area representing 

 these parts of the body (Mills). On the mesial surface of the cerebrum there 

 are sensor areas for a portion of the leg, anus, genitalia and viscera. 



The afferent pathway through which the nerve impulses, developed in 

 the sense-organs of the skin, tendons and muscles, pass to the cortical areas 

 and evoke the characteristic sensations has been described on pages 544 

 and 545. 



3. The Stereo gnostic Area. The area of stereognostic perception. Stereog- 



nosis is the recognition of an object when placed in the hands, through 

 its form, density, temperature, etc. The area associated with stereog- 

 nostic perception has been assigned to a portion of the super-parietal 

 convolution and to the precuneus. 



This perception depends on the integrity and cooperation of the tactile, 

 the pressure, the temperature and muscle senses as well as the power of dis- 



