REPORT ON THE SEALS. 125 



olfactory apparatus. When that is large the Sylvian fissure is shallow, but when the 

 olfactory peduncle and roots diminish in size, as in the Seal and Walrus, the fissure 

 deepens and the Sylvian convolution becomes partially concealed, untd in Apes and 

 Man, with a still greater diminution in the importance of the olfactory sense, the fissure 

 attains its maximum depth. In this connection, however, it must be remembered that 

 the Polar Bear, though with an arched convolution concealed within the Sylvian fissure, 

 yet possesses large olfactory nerve roots. 



This view of the homology of the convolutions in this region enables one to harmonize 

 the results of physiological experiment with anatomical arrangement, and to remove a 

 difficulty which is experienced so long as the superior temporo-sphenoidal convolution 

 is regarded as corresponding with the posterior limb of the Sylvian convolution. Dr. 

 Ferrier, from his experiments, determined that the areas marked (14) in his figures 

 were the auditory centres. Thus when these areas in the superior temporo-sphenoidal 

 convolution were stimulated in Monkeys the opposite ear became pricked, the head and 

 eyes were turned to the opposite side and the pupds became widely dilated ; whilst 

 stimulation of areas (14) in the 3rd external convolution of the brain of the Dog and 

 Jackal also produced a pricking or retraction of the opposite ear, and stimulation of a 

 similar area in the Cat produced both pricking of the opposite ear and turning of the 

 head and eyes to the opposite side. Hence these areas in the carnivorous and Ape's 

 brain are regarded as physiologically the same ; though in the Ape the convolution 

 stimulated bounds the Sylvian fissure, whfist in the Carnivora it is separated from that 

 fissure by an intermediate convolution. On the theory that the Sylvian convolution 

 either becomes the Island of Eeil or blends with the insula and sinks into the fissure, the 

 3rd external convolution would then become the boundary of the fissure and its posterior 

 limb would be homologous with the superior temporo-sphenoidal convolution of the brain 

 of Man and Apes, whilst the suprasylvian or 3rd curved fissure would become lost in the 

 Sylvian fissure, and be represented by the sulcus insulae. This theory is somewhat 

 different from the conception of the relation of parts in this region entertained by 

 Ferrier, who suggests that the Sylvian convolution is in the Monkey's brain represented 

 within the lips of the Sylvian fissure, overlapping and concealing the Island of Reil. 



Ferrier has also shown that electrical stimulation of the posterior limb of the Sylvian 

 convolution gives no definite reactions, and similarly stimulation of the Island of Reil 

 is not followed by movements except after increased irritation, when some move- 

 ments of the mouth and tongue occur, which he considers may be due to conduction 

 of the stimulus to the motor areas situated immediately anterior to the part irritated. 

 Ordinary stimulation in both instances therefore produces no definite results, showing 

 that neither of these convolutions responds to the electrical stimulus, and although the 

 experimental result is negative, it is certainly not adverse to the view that they are 

 homologous with each other. Confirmation of this theory is also furnished by the fact 



