COMPOSITION AND CENTRAL CONNECTIONS OF CRANIAL NERVES 869 



Broca] and course backward in the longitudinal stria? to the dentate gyrus and 

 the hippocampal region. The indusium is usually considered as a rudimentary 

 part of the rhinencephalon. 



The olfactory projection fibers which arise from the pyramid cells of the uncus and 

 hippocampus and from the polymorphic cells of the dentate gyrus form a dense 

 stratum on the ventricular surface, especially on the hippocampus, called the alveus. 

 These fibers pass over into the fimbria and are continued into the fornix. About 

 one-fourth of all the fibers of the fimbria are large projection fibers, the other three- 

 fourths consist of fine commissural fibers which pass from the hippocampus of one 

 side through the fimbria and hippocampal commissure (central psalterium or lyre), 

 to the fimbria and hippocampus of the opposite side where they penetrate the pyram- 

 idal layer and terminate in the stratum radiatum. The fibers which course in the 

 fornix pass forward and downward into the corpora mammillare where numerous 

 collaterals are given off and a few terminate. Most of the fibers in the fornix, 

 however, pass through the corpora, cross the middle line and turn downward in 

 the reticular formation in which they are said to be traceable as far as the pons and 

 possibly farther. As the fornix passes beneath the corpus callosum it receives 

 fibers from the longitudinal striae of the indusium and from the cingulum; these are 

 the perforating fibers of the fornix which pass through the corpus callosum and 

 course in the fornix toward the mammillary body. As the fornix passes the anterior 

 end of the thalamus a few fibers are given off to the stria medullaris of the thalamus 

 and turn back in the stria to the habenular ganglion of the same and the opposite 

 side, having probably the same relation that the reflex fibers have which arise from 

 the primary centers and course in the stria medullaris of the thalamus. Aside from 

 the fibers of the fornix which pass through the mammillary body to decussate and 

 descend (as the mammillo-mesencephalic fasciculus), many fibers are said to pass 

 into the bundle of Vicq d'Azyr, and one bundle of fibers is said to pass from the 

 fornix to the tuber cinereum. 



The mammillary bodies receive collaterals and terminals then from the cortical 

 centers via the fornix and probably other collaterals and terminals are received 

 directly from the primary centers through the tractus olfactomesencephalicus. 

 According to Cajal fibers also reach the mammillary body through the peduncle 

 of the corpus mammillare from the arcuate fibers of the tegmentum and from the 

 main fillet. The fornix probably brings the cortical centers into relation with the 

 reflex path that runs from the primary centers to the mammillary body and the 

 tuber cinereum. 



The bundle of Vicq d'Azyr (mammiUo-thalamic fasciculus') arises from cells in both 

 the medial and lateral nuclei of the mammillary body and by fibers that are directly 

 continued from the fornix. There axons divide within the gray matter; the coarser 

 branches pass into the anterior nucleus of the thalamus as the bundle of Vicq d'Azyr, 

 the finer branches pass downward as the mammillo-tegmental bundle of Gudden. 

 The bundle of Yicq d'Azyr spreads out fan-like as it terminates in the anterior 

 or dorsal nucleus of the thalamus. A few of the fibers pass through the dorsal 

 nucleus to the angular nucleus of the thalamus. The axons from these nuclei are 

 supposed to form part of the thalamocortical system. 



The mammillo-tegmental bundle has already been considered under the olfactory 

 reflex paths. 



The amygdaloid nucleus and the tsenia semicircularis (stria terminalis) probably 

 belong to the central olfactory apparatus. The ta?nia semicircularis extends from 

 the region of the anterior perforated substance to the nucleus amygdalae. Its 

 anterior connections are not clearly understood. Fibers are said to arise from cells 

 in the anterior perforated substance ; some of the fibers pass in front of the anterior 

 commissure, others join the fornix for a short distance as they pass behind the 

 anterior commissure. The two strands ultimately join to form the taenia and pass 



