





COMPOSITION AND CENTRAL CONNECTIONS OF CRANIAL NERVES 867 



form the olfactory tract. The olfactory tract is continued into the olfactory 

 trigone, just in front of the anterior perforated substance. The axons of the mitral 

 cells on reaching the olfactory trigone separate into three bundles, the lateral 

 olfactory stria, the medial olfactory stria and the less marked intermedia! olfactory 

 stria. 



The lateral olfactory striae curve lateralward, a few of the fibers end in the 

 olfactory trigone and the antero-lateral portion of the anterior perforated substance. 

 Most of the fibers, however, pass into the uncus, the anterior end of the hippo- 

 campal gyms, and there end in the complicated cortex of the hippocampal gyri. 

 The lateral strise more or less disappear as they cross the antero-lateral region of 

 the anterior perforated substance. 



The greater mass of the fibers of the olfactory tract pass into the lateral stria. 

 Numerous collaterals are given into the plexiform layer of the subfrontal cortex, 

 over which the strise pass on their way to the uncus, where they intermingle with 

 the apical dendrons of the medium-sized and small pyramidal cells of the pyramidal 

 layer of this subfrontal or frontal olfactory cortex. The axons give rise to projection 

 fibers which take an antero-posterior direction to the subthalamic region sending 

 collaterals and terminal branches to the stria medullaris and others toward the 

 thalamus. Some of the fibers extend farther back and are believed to reach the 

 pons and medulla oblongata. 



Most of the fibers of the lateral olfactory stria pass to the hippocampal region 

 of the cortex, especially to the gyrus hippocampi, which may be regarded as the 

 main ending place of the secondary olfactory path derived from axons of the mitral 

 cells. 



The fibers of the medial olfactory striae terminate for the most part in the par- 

 olfactory area (Broca's area), a few end in the subcallosal gyrus and a few in the 

 anterior perforated substance and the adjoining part -of the septum pellucidum. 

 Some of the fibers pass into the anterior commissure (pars olfactoria) to the olfac- 



fly tract of the opposite side where they end partly within the granular layer 

 and partly in the neighborhood of the glomeruli of the olfactory bulb, thus con- 

 necting the bulbs of the two sides. 



The intermediate olfactory striae are as a rule scarcely visible, the fibers terminate 

 in the anterior perforated substance, a few are said to continue to the uncus. 



The trigonum olfactorium, anterior perforated substance and the adjoining 

 part of the septum pellucidum are important primary olfactory centers, especially 

 for olfactory reflexes; in these centers terminate many axons from the mitral cells 

 of the olfactory bulb. In addition the gray substance of the olfactory tract and the 

 gyrus subcallosus receive terminals of the mitral cells. 



The pathways from these centers to lower centers in the brain-stem and spinal 

 cord are only partially known. The most direct path, the tractus olfactomesen- 

 cephalicus (basal olfactory bundle of Wallenburg), is supposed to arise from cells in 

 the gray substance of the olfactory tract, the olfactory trigone, the anterior per- 

 forated substance and the adjoining part of the septum pellucidum. The fibers 

 are said to pass direct to the tuber cinereum, to the corpus mammillare, to the brain- 

 stem and the spinal cord. The fibers which enter the mammillary body probably 

 come into relation with cells whose axons give rise to the fasciculus mammillo- 

 tegmentalis (mammillo-tegmental bundle of Giidderi) which is supposed to end in 

 the gray substance of the tegmentum and of the aqueduct; some of its fibers are 

 said to join the posterior longitudinal bundle and others to extend as far as the 



ticular formation of the pons. 



Some of the fibers of the medial olfactory stria came into relation with cells 

 n the parolfactory area of Broca and in the anterior perforated substance, whose 

 axons course in the medullary stria of the thalamus. As the axons pass through 

 the lower part of the septum pellucidum they are joined by other fibers whose cells 



