1222 



HUMAN ANATOMY. 



Central and Cortical Connections.— The impulses conveyed by the olfactory nerves and 

 received by the mitral cells of the olfactory bulb, which cells may be regarded as constituting 

 the end-station or reception-nucleus of the peripheral path, are carried to neurones situated either 

 within the gray matter of the olfactory tract, the anterior perforated space or the adjacent part 

 of the septum lucidum (Fig. 1049). Fibres connecting the olfactory centres of the two sides pro- 

 ceed from the cortex of the tract by way of the anterior commissure, forming the pars olfactoria 

 of the latter, to end in relation with the cells within the opposite tract or bulb. From these 

 primary centres the impulses are transmitted by different paths to the secondary or cortical 

 centres situated in the anterior part of the hippocampal convolution in the vicinity of its uncus, 

 including the hippocampus major and the nucleus amygdalae. 



I. The most direct path is by way of the lateral root of the olfactory tract (page 1153), by 

 which fibres from cells within the trigonum olfactorium pass, skirting the Sylvian fissure, to the 

 anterior part of the gyrus hippocampi to terminate in relation with the cortical cells of that 

 convolution. 



Fig. 1049. 



Diagram showi no; nio=;t important connections of olfactory tracts ; LC lamina cribrosa ; /?, olfactory bulbs ; TV, 

 olfactory tract ; 7]^, olfactory trigone ; Ai, 71/j, lateral and mesial striae ; /}, anterior commissure ; CC. corpus callo- 

 sum ; SL, septum lucidum; Fx, anterior pillar of fornix; M, mammillary body; m-t , mammillo-thalamic tract ; 

 /4/', anterior perforated space; 7i^»/,'taeniasemicircularis; 7", thalamus; T^w, fimbria descending on hippocampus; 

 U, uncus ; AN, amygdaloid nucleus ; 7X, temporal lobe. 



2. Fibres from the cells within the olfactory trigone (page 1153) and the anterior perfo- 

 rated space (page 1 153) pass into the septum lucidum and, reinforced by others from cells of the 

 septum, enter the fornix ; thence continuing backward and downward by way of the fimbria 

 they reach the hippocampus major. 



3. Fibres from cells within the olfactory trigone turn inward and by way of the medial root 

 of the olfactory tract gain the gyrus subcallosus ; thence they pass along the upper surface of the 

 corpus callosum within its longitudinal striae and descend by way of the dentate gyrus to reach 

 the anterior end of the hippocampus major. 



4. Fibres from cells within the anterior perforated space and septum lucidum, joined by 

 accessions from the opposite olfactory tract by way of the anterior commissure, converge to the 

 taenia semicircularis (page 1162) and, passing along the floor of the lateral ventricle, descend 

 within the roof of the descending horn to end in the amygdaloid nucleus (Dejerine). During 

 their ascent from the anterior perforated space, some fibres diverge almost at right angles and 

 pass backward directly to the optic thalamus. The connections between the cortical centres of 

 olfaction and the optic thalamus, as well as those between the olfactory centres of the two 

 sides, by way of the fornix, are described on page 1167. 



Practical Considerations. — Lesions of the uncinate gyrus may cause loss 

 of the sense of smell on one or both sides. Paralysis of the olfactory nerve with loss 

 of smell may also occur in fractures of the base of the skull in the anterior fossa, 

 involving the cribriform plate. 



