Functions of the Cerebrum. 661 



bral expansion of the pyramidal tracts and the destruction of these parts 

 alone leads to the degeneration or atrophy of the pyramidal tracts. Each 

 particular bundle of the pyramidal nerves has its definite corresponding 

 patch of cortical cells and suffers atrophy only when such definite patch 

 is destroyed. 



FIG. 367. Base of right hemisphere of Monkey. 



15. Anterior and inner aspect of Uneinate Gyms 

 or Subiculum Cornu Ammonis. 



This is the motor area of smell in the torsion of the 

 lip and partial closure of the nostril on same side. 



The olfactory tract of nerves coming in 

 from the olfactory lobe divides into two 

 branches, the inner and the outer root ( see 

 fig. 270 ) separated by a triangular space. 

 The inner root joins the mesial aspect of 

 the anterior end of the gyrus fornicatus 

 (fig. 366 Gf). The outer root passes out- 

 ward to the extremity of the tempero sphe- 



noidal lobe where it fuses with the anterior 







extremity of the gyrus hippocampi ( under 

 15 fig. 367, also #fig. 366 ). In the dog 

 and other acute smelling animals this part 

 of the hemisphere forms a prominent bulb 

 (15 fig. 367 ) and is called the natiform protuberance, pyriform lobe, or 

 hippocampal lobule. This lobule is the cortical organ of smell for the 

 same side. 



Speech. The reference figure 9 in figs. 361 and 362 rests upon a lip 

 or shell of brain substance beneath which is another layer of brain, hav- 

 ing in men and monkeys short radiating convolutions called gyri breves. 

 This portion of brain is called the Island of Reil. Fig. 350 will help to 

 show its position and fig. 267 its form. This Island of. Reil and the 

 patch of brain which overlaps it on the outside are concerned in the 

 motor actions that are involved in the faculty of speech. In this por- 

 tion of the brain those special combinations of motor stimuli are effected 

 which are essential to the production of articulation. There are other 

 centers from which the muscles of the face or those of the jaws, or of the 

 tongue, of the larynx and of the nose can be worked separately or in 

 partial combination for various purposes, but the nervous combinations 

 necessary for uttering definite articulate sounds are made up in this 

 region. 



It is a curious fact in most right-handed persons, the Island of Reil 

 on the left side only is actively functional, while in left-handed persons 

 this part of the right side has been observed in many cases to assume 

 the whole supervision of articulation to the exclusion of the left side. 



FIG. 367. 



