THE VISCERAL AFFERENT DIVISION. 171 



cephali. These may serve the more fully to bring about correlations 

 with the somatic muscles in addition to the connections in the 

 funicular region. From the inferior lobes two tracts already 

 well known in lower vertebrates may forAvard the gustatory impulses. 

 One of these is the tractus lobo-bulbarls which runs back through 

 the myelencephalon and makes connections with the motor nuclei 

 of the cranial nerves. The second tract is the Ir actus lobo-epi- 

 siriaticus which carries impulses to that large coordinating center 

 of the forebrain (epistriatum) which is primarily a part of the 

 olfactory apparatus and in amphibia, reptiles and mammals 

 develops into the hippocampal lobe and adjacent parts of the 

 true olfactory cortex. (See Chapter XVIII.) It is possible that 

 this tract is retained in higher vertebrates and serves as the path 

 of gustatory sensations in the true sense. The chief central 

 gustatory connections are shown in Figs. 89 and 90. 



The arrangement of the secondary gustator}^ tracts and nuclei 

 in selachians throws light on certain important structures peculiar 

 to the brain of ganoids and teleosts. In both these classes the 

 superior secondary gustatory nucleus is large, lies in the lateral 

 wall of the metencephalon and sends its commissure through a 



Fig. 89. — A parasagittal section through the brain of the spotted sucker, Miny- 

 trema melanops, to show the gustatory centers and tracts. From C. Judson 

 Herrick. 



The sketch is designed to illustrate the course of the ascending secondary 

 gustatory tract and the connections of its terminal nucleus. The plane of the 

 section is slightly oblique so that the caudal end and the ventral side are nearer the 

 median line than are the cephalic and dorsal borders. The figure is a composite, 

 made by outlining one section with the camera lucida and filling in the details from 

 this section and the three sections of the same series on each side immediately 

 adjacent, omitting irrelevant detail. The features introduced are schematized as 

 little as possible. The whole course of the ascending secondary gustatory tract 

 from the facial lobe is shown. The origin of the tract from the vagal lobe lies 

 farther lateral. 



b., tract between secondary gustatory nucleus and n. lateralis valvulae; com.h., 

 commissura horizontalis, Fritsch; com. r. VII, communis (gustatory) root of the 

 facialis; desc.sec.X, descending secondary gustatory tract from the vagal lobe; f.l.m., 

 fasciculus longitudinalis medialis; inj.lob.lat., lateral lobule of inferior lobe 

 (hypoaria, C. L. Herrick); inf.lob.m., median lobule of inferior lobe (mammil- 

 lare, C L. Herrick); n.cort., nucleus corticalis, Fritsch; n.IX, motor nucleus of 

 the glossopharyngeus; n.lat., nucleus lateralis valvulae; n.rot., nucleus rotundus, 

 Fritsch; n.st., nucleus subthalamicus, C. L. Herrick; n.V, motor nucleus of the 

 trigeminus; n.VII, motor nucleus of the iac[a.lis;r.X.s., sensory root fibers of the 

 vagus; sec. gust. t., ascending secondary gustatorj' tract from the facial and vagal 

 lobes; tr.l.b., tractus lobo-bulbaris; tr.t-c, tractus tecto-cerebellaris; tr.t-lob., tractus 

 tecto-lobaris, Johnston (commissura vehtralis, C. L. Herrick). The area marked 

 n.junicidi contains also the inferior secondary gustatory nucleus. 



