6o 4 TEXT-BOOK OF PHYSIOLOGY 



that the so-called motor and sensor areas are so closely related that it is 

 almost impossible to distinguish one from the other either anatomically or 

 physiologically. Thus the Rolandic region is believed to be both motor and 

 sensor in function, the former, however, being more predominant in the pre- 

 central, the latter in the post-central, convolution. As these two functions 

 are so intimately blended and their anatomic substrata so difficult of separa- 

 tion, it is thought the term sensori-motor should be employed as more descrip- 

 tive and more in accordance with the facts to the entire Rolandic region. 



This view has been strengthened by the results of the embryologic 

 investigation of Flechsig, which show that different nerve-tracts become 

 medullated or receive their myelin investment at successively later periods and 

 that the tracts which first become myelinated and are hence first functionally 

 active, belong to the afferent system. Among the first to undergo myelini- 

 zation are three tracts numbered by Flechsig i, 2 and 3, which arise largely 

 from the median nucleus of the thalamus and the medial lemniscus and pass 

 to the anterior and posterior convolutions, to the para-central lobule and 

 foot of the superior frontal convolution, and to the foot of the third frontal 

 convolution respectively. It is these fibers which convey nerve impulses to 

 the cortex and furnish information regarding changes taking place in the 

 body itself and thus lead to the performance of muscle movements. This 

 area is therefore primarily a sensor area, an area for body-feelings, cutaneous, 

 tactile, muscle, and visceral, and secondarily a motor area. The afferent 

 fibers to this region become myelinated during the ninth month of intra- 

 uterine life, the efferent fibers from it become myelinated during the third 

 month of extra-uterine life. 



By the same method of reasoning the gustatory, olfactory, auditory, and 

 visual sense areas are to be regarded as sensori-motor in character, for embryo- 

 logic investigations show that subsequently to the myelinization of the 

 afferent tracts connecting the sense-organs with the cortex, efferent nerve- 

 tracts arise from or near to the same centers and undergo myelinization. In 

 other words, these areas are primarily sensor and secondarily motor, and 

 therefore should be termed sensori-motor. In Flechsig's own terminology 

 each corticopetal or afferent tract is accompanied by a corticofugal or efferent 

 tract. 



The view, viz. : the coincidence of sensor and motor areas has had general 

 acceptance for the reason that it seemed more in accordance with the facts 

 than the earlier view. Nevertheless there were many facts both of a physio- 

 logic and pathologic character which were difficult to harmonize with it, and 

 in recent years the accumulation of facts and the weight of evidence inclines 

 toward the view that the areas are anatomically separate and distinct though 

 associated functionally. 



The motor speech and the motor writing areas will be considered in the 

 following paragraphs. 



Language. Language may be defined as the expression of ideas by a 

 succession of motor acts and may be divided into (i) spoken language (ar- 

 ticulate speech), and (2) written language. The expression of ideas by 

 words (speech) and by verbal signs (writing) depends primarily on the power 

 of reviving images or memories of objects, words, letters, numbers, etc., seen 

 and heard, and secondarily on the power of reviving the images or memories 

 of the muscle movements which were previously employed in an effort to 



