44 



PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



optic lobes, into which the optic roots are seen to enter. 

 But in many cases we consciously observe and remem- 

 ber the impressions of sight — form mental images of 

 objects seen. In such cases the impression is sent on 

 from the thalamus to the cerebrum. The area to which 

 these impressions are sent — visual area — is situated in 



VMpJi. 



Fig. 29. — Functional areas of the cerebrum : m % motor of the body ; j, sen- 

 sory of the body ; v, visual ; olf, olfactory areas ; aph, motor aphasia 

 ( speech 1; a.aph, auditory aphasia; v. aph, visual aphasia (reading;; 

 g.aph, graphic aphasia (writing). 



the posterior lobes and marked v. Similarly, auditory 

 areas are marked a.a, general sensation areas by s, gen- 

 eral motor areas by m, and olfactory areas by olf. 



One of the most curious and interesting of these 

 discoveries is that of the speech area, aph. This, of 

 course, was discovered by observation on man — not 

 experiments on animals. It has been long observed 

 that there are cases in which a patient is perfectly intel- 

 ligent and knows what he wants to say, but can not say 

 it. Such an affection is called aphasia. In such cases it 

 is invariably found by post mortem that there is a lesion 

 of a particular convolution of the frontal lobe, especially 

 of the left side. 



