(2) _Cortical Ablations._ When the cortical spot which is found to produce a movement of the fore-leg, in a dog, is excised (see spot 5 in Fig. 5), the leg in question becomes peculiarly affected. At first it seems paralyzed. Soon, however, it is used with the other legs, but badly. The animal does not bear his weight on it, allows it to rest on its dorsal surface, stands with it crossing the other leg, does not remove it if it hangs over the edge of a table, can no longer 'give the paw' at word of command if able to do so before the operation, does not use it for scratching the ground, or holding a bone as formerly, lets it slip out when running on a smooth surface or when shaking himself, etc., etc. Sensibility of all kinds seems diminished as well as motility, but of this I shall speak later on. Moreover the dog tends in voluntary movements to swerve towards the side of the brain-lesion instead of going straight forward. All these symptoms gradually decrease, so that even with a very severe brain-lesion the dog may be outwardly indistinguishable from a well dog after eight or ten weeks. Still, a slight chloroformization will reproduce the disturbances, even then. There is a certain appearance of ataxic in-coordination in the movements--the dog lifts his fore-feet high and brings them down with more strength than usual, and yet the trouble is not ordinary lack of co-ordination. Neither is there paralysis. The strength of whatever movements are made is as great as ever--dogs with extensive destruction of the motor zone can jump as high and bite as hard as ever they did, but they seem _less easily moved_ to do _anything_ with the affected parts. Dr. Loeb, who has studied the motor disturbances of dogs more carefully than any one, conceives of them _en masse_ as effects of an increased inertia in all the processes of innervation towards the side opposed to the lesion. All such movements require an unwonted effort for their execution; and when only the normally usual effort is made they fall behind in effectiveness.[11] [Illustration: FIG. 5.--Left Hemisphere of Dog's Brain, after Ferrier. _A_, the fissure of Sylvius. _B_, the crucial sulcus. _O_, the olfactory bulb. _I, II, III, IV,_ indicate the first, second, third, and fourth external convolutions respectively. (1), (4), and (5) are on the _sigmoid_ gyrus.] [Illustration: FIG. 6.--Left Hemisphere of Monkey's Brain. Outer Surface.]