526 



TEXT-BOOK OF PHYSIOLOGY. 



and consists of bqth_graiy_and white matter. 



platejpf the ethnioid_borie and is embraced by the ollactory nerves. 

 As seen on sagittal section, there is just beneath the surface a layer 

 of large pyramidal and spindle-shaped cells (termed also mitral cells), 

 each provided with an apical and two, lateral dgndrites. The apical 

 dendrite passes toward the~surface and ends in a brush- or basket-like 

 expansion which interlaces with the end-tufts of the olfactory nerves, 



forming what are 

 known as the olfac- 

 tory glomerules. The 

 lateral dendrites end 

 free. 



The axons of the 

 pyramidal cells pass 

 toward the center of 

 the bulb and bend at 

 right angles, after 

 which they pursue a 

 horizontal direction 

 toward and into the 

 olfactory tract. This 

 tract is about five 

 centimeters in length, 

 prismatic in shape on 

 cross-section and di- 

 visible into a ventral 

 and a dorsal portion. 

 It emerges from the 

 FIG. 239. OLFACTORY LOBE OF THE HUMAN BRAIN. posterior extremitv of 

 Bu. Olfactory bulb. T. Tract. Tr.o. Trigone. R. f, Ki ilK 

 Rostrum of corpus callosum. p. Peduncl! of cor- the bulb > P aSSCS back - 

 pus callosum, passing into G.s., gyrus subcallosus Ward to the posterior 

 (diagonal tract, Broca). Br. Broca's area. P.p. 

 Fissura prima. F.s. Fissura serotina. C.a. Posi- 

 tion of anterior commissure. L.t. Lamina ter- 

 minalis. Ch. Optic chiasma. T.o. Optic tract. 



p.olf. Posterior olfactory lobule (or anterior per- 

 forated space). ih.r. Mesial root. l.r. Lateral 

 root of tract. (His.} (After Quain.} 



part of the anterior 

 lobe, where it divides 

 into three roots: viz., 

 a lateral or external, 

 a mesial or internal, a 

 middle or dorsal. The 

 fibers of the lateral and mesial roots are derived almost exclusively 

 from the ventral portion of the tract, the fibers of which come from the 

 mitral cells in the bulb. The lateral root-fibers pass outward into the 

 fossa of Sylvius and come into relation with nerve-cells in the inferior 

 extremity of the gyrus hippocampus and the gyrus uncinatus. The 

 mesial fibers pass inward and come into relation with nerve- cells 

 in the pre-callosal part at least of the gyrus fornicatus. The fibers 

 thus far considered are undoubtedly true olfactory fibers, pursuing 



