668 PHYSIOLOGY OF THE CEREBRUM 



intermediary regions there are fewer projection fibers than in the primordial 

 regions. Individual fibers indeed are to be demonstrated, but they are very 

 scarce as compared with those in other tracts. 



The terminal regions, on the other hand, are richest in association fibers, 

 that is, in fibers running from one region of the cortex to the other; in fact 

 they may be said to constitute the nodal points of the long association systems. 

 But there are no long systems to be found which can be said to unite any two 

 primordial regions regarded as sensory centers. A visual and an auditory im- 

 pression, for example, could not meet in a primordial center: this could only 

 happen in one of the intermediary or terminal regions. 



The last named therefore constitute association centers. Three regions 

 in each hemisphere are embraced by them, namely, a frontal or anterior, an 

 insular or middle, and a parieto-occipito-temporal or posterior region. There 

 is no reason to believe that these three are of equal importance for the 

 psychical functions; in fact their positions with reference to the different 

 sensory areas would seem to indicate that they have special functions. The 

 posterior association center is intercalated between the visual, the auditory 

 and the tactile areas; the anterior between the tactile and the olfactory 

 probably also the gustatory areas; the middle between the auditory, the 

 olfactory and the tactile areas. 



The anterior center is formed by the anterior half of the first and the 

 greater part of the second convolutions. On the basal side of the frontal lobe 

 the gyrus rectus particularly belongs to this center. The middle center covers 

 the insula. The posterior center embraces the pre'cuneus, the parietal con- 

 volutions, parts of the lingual gyrus, the fusiform gyrus, the second and 

 third temporal and the anterior portions of all three occipital convolutions 

 (see Figs. 293 and 294). 



B. THE ANTERIOR ASSOCIATION CENTER 



We have already learned from observations on animals that extirpation of 

 the frontal lobes produces noteworthy alterations in the intelligence and char- 

 acter of the animal. After removal of the most anterior portion of the brain, 

 dogs become exceedingly irritable. Harmless, good-natured animals become 

 fierce and malicious, so that after the operation they will not even allow them- 

 selves to be touched. The animal's movements are exceedingly cumbrous and 

 awkward. He cannot hold a bone firmly, his whole carriage of himself is un- 

 steady, he stumbles easily and on a slippery floor at once loses his footing (Goltz). 



In line. with this, Bianchi has observed that the intelligence with which a 

 monkey performs complicated acts is often greatly affected by the removal of 

 both frontal lobes. 



Similar changes in character have not infrequently been observed in men 

 with lesions of the frontal convolutions. Persons, who before were well dis- 

 posed and orderly, became foolish, impatient and headstrong, and at the same 

 time changeable and fickle. Neither sensory nor motor disorders of any kind 

 can be demonstrated on them (Welt). 



Flechsig has given the following description of the effects of lesions in 

 the frontal association centers observed on men. The patient sometimes loses 



