238 TRE CEREBRUM. 



motor centers. In this manner the writing center is connected 

 with the motor center for the upper extremity, and the speech 

 center with the motor centers for the lips, tongue, etc.: breaking 

 of the former connection on the left side destroys ability to write, 

 agraphia; and aphasia results, if the latter connection is broken. 

 Besides these and many other connections of associated centers, 

 the short fibers join together the various parts of each cortical 

 area. 



The long association fibers (Figs. 74 and 75) are collected 

 into bundles. They rise from the pyramidal, the polymorphous 

 and the fusiform layers of the cerebral cortex (Cajal), and are 

 axones. Proceeding out of the lobe in which they rise, being 

 interlobar, they dip down into the centrum semiovale and arborize 

 about neurones in more or less distant parts of the cortex. Among 

 the best known are the following bundles: 



(1) The cingulum of the gyrus fornicatus (Fig. 74) is a bundle 

 of fibers in that gyrus which almost entirely encircles the corpus 

 callosum. It extends from the anterior perforated substance 

 through the gyrus cinguli and hippocampal gyrus, to the uncus 

 and temporal pole. The fibers, which form several systems, 

 have been divided into three groups by Beevor, namely: (a) The 

 anterior, which joins the region of the anterior perforated sub- 

 stance to the fore part of the frontal lobe, (b) The horizontal, 

 which unites the frontal lobe and the gyrus fornicatus. (c) The 

 posterior fasciculus, which associates the lingual and fusiform 

 gyri with the hippocampal gyrus and the pole of the temporal 

 lobe. Like the two following bundles it establishes associations 

 for the sense of smell. 



(2) The Fornix (Fig. 74). In each lateral half of the fornix 

 is a bundle of association fibers as well as of projection and com- 

 missural fibers. The projection fibers rise in the olfactory bulb 

 and in the region of the olfactory triangle and, running up through 

 septum pellucidum to the fornix, continue through it to their 

 destination in the hippocampus and uncus. The commissural 

 fibers of the fornix rise in the uncus, the fascia dentata and gyrus 

 hippocampi and run through the alveus of the hippocampus into 

 the crus fornicis, whence they cross through the commissura hip- 



