THE CEREBRUM 9 



surface of the brain at the lateral side of the anterior per- 

 forated substance (ant. p erf. spot} (p. 16) and passes laterally, 

 separating the temporal from the frontal lobe. When it 

 reaches the lateral surface of the brain, it divides into three 

 rami. The anterior horizontal and the anterior ascending 

 rami pass forwards and upwards, respectively, into the inferior 

 frontal gyms, and the cortical areas which surround them 

 constitute the area of Broca. The motor speech centre is 

 situated in this area, on the left side of the brain in right- 

 handed subjects and on the right side of the brain in left- 

 handed subjects. Cortical lesions of Broca's area cause 

 motor aphasia, but, if the lesion is localised, the patient can 

 understand what is said to him and can read and write 

 intelligently. 



The posterior ramus of the lateral fissure runs backwards, 

 separating the frontal and parietal lobes above from the 

 temporal lobe below, and finally it turns upwards to end in the 

 parietal lobe. At its termination it is surrounded by the 

 supramarginal gyrus, which lies under cover of the parietal 

 tuber (eminence] (Fig. 4). 



The Superior Temporal Sulcus lies in the temporal lobe below 

 and parallel to the posterior ramus of the lateral fissure, and it 

 also turns upwards to end in the parietal lobe. Its extremity 

 is surrounded by the angular gyrus, which contains the visual 

 speech centre. In cortical lesions of this gyrus, the patient 

 cannot understand written or printed matter, although other- 

 wise his vision may be quite unaffected and he can speak and 

 write intelligibly. The latter action may be carried out with 

 difficulty, as he cannot appreciate whether he is writing sense 

 or nonsense. 



The Superior Temporal Gyrus lies between the posterior 

 ramus of the lateral fissure above and the superior temporal 

 sulcus below. It contains the higher auditory and word- 

 hearing centres and, when involved in pathological conditions, 

 it gives rise to partial deafness of the opposite ear (p. 89). 



The Superior Parietal Gyrus is a strip of cortex which is 



