326 THE BRAIN OF THE TIGER SALAMANDER 



the reader in comparing the amphibian topography with the conventional mammalian analy- 

 sis. Median structures, that is, the cut surfaces of the section, are outlined with full lines, 

 paramedian structures in dotted lines (compare the gross section, fig. IB; Necturus, '17, fig. 

 63; and McKibben, '11, fig. 5). Heavy broken lines mark the boundaries of the larger divisions 

 as here defined, and dot-and-dash lines mark the subdivisions of the diencephalon. 



B. — The same outline, bearing names of some of the smaller subdivisions. The scales at 

 right and left indicate the approximate planes of the sections shown in figures 25-36. These 

 levels are not exact, for unequal shrinkage during preparation produced some irregularities 

 which have been smoothed in the diagram. The scales at top and bottom show section num- 

 bers of the type specimen, no. IIC, from which figure 2C was drawn, as indicated on that 

 figure. Here again the correspondence is not exact, though sufficiently close to facilitate orienta- 

 tion of the published transverse sections with reference to the two median sections. 



C- — This is the median section of the type specimen, IIC (p. 321), copied from 1935a, 

 figure 1, with some changes in the lettering. X 30. 



Figure 3. — Outline drawing of the dorsal surface of the adult brain. X 10. The paraphysis 

 and chorioid plexus of the fourth ventricle have been removed. The courses of the .sensory 

 fibers of the trigeminal and dorsal spinal nerve roots and of the spino-bulbar, spino-cerebellar, 

 and spinal lemniscus secondary tracts are diagrammatically indicated. The general bulbar 

 lemniscus {Im. of the other figures) arises from the entire sensory zone of the medulla oblongata 

 and ascends approximately parallel with the spinal lemniscus. 



Figures 4 and 5. — Two diagrams illustrating the extent of the sensory and motor zones as 

 seen in horizontal sections of the adult brain (chap. v). X 15. The outlines are from a series 

 of Cajal sections cut in a slightly different plane from those illustrated in figures 25-36, with 

 the anterior end more dorsal. 



Fig. 4. — This passes through the hippocampal commissure and shows on the left side the 

 extent of the motor zone, as here defined, by oblique hatching and the sensory zone in the 

 olfactory area by hatching in the reverse direction. The plane of section is about the same as 

 that of figures 28 anteriorly and 27 posteriorly. It passes below the tuberculum posterius at the 

 cerebral flexure, above which the motor zone of the peduncle and isthmus is continuous be- 

 tween the medulla oblongata and the ventral thalanms (fig. 30). 



Fig. 5. — This shows the extent of the sensory zone at a more dorsal level, the plane being 

 about that of figures 35 anteriorly and 34 posteriorly. The undifferentiated anterior olfactory 

 nucleus encircles the base of the olfactory bulb, and through it passes the very large fasciculus 

 postolfactorius (cf. fig. 105), from wliich tlie various olfactory tracts of the liemisphere are 

 distributed (p. 55; '27, p. 283). 



Figure 6. — Selected examples of long pathways of conduction leading toward the skeletal 

 musculature of the trunk and limbs, seen as projected upon the lateral aspect of the brain. 

 X 10. The only afferent systems drawn are the olfactory and optic, and from these receptive 

 fields only a few lines of descending conduction are indicated as typical representatives of 

 through fore-and-aft transmission. 



Figure 7. — Diagram of the central courses of the sensory components of cranial nerves 

 V to X of larval Amblystoma seen as projected upon the lateral surface of the medulla ob- 

 longata. X 36. The drawing is based on figure 3 of 1914. The general cutaneous component 

 is drawn in dashed lines, the vestibular in thick unbroken lines, the visceral-gustatory in 

 dotted lines, the three lateral-line VII roots in thick dash lines, the two lateral-line X roots 

 in dot-and-dash lines, and correlation tracts a and b in thin continuous lines. Some fibers of 

 the ascending roots of the general cutaneous and vestibular systems decussate in the cerebel- 

 lum, and some visceral root fibers of the f. solitarius decussate in the commissura infima at 

 the commissural nucleus of Cajal. 



Figure S.— Diagram of the central connections of the visceral-gustatory system seen as 

 projected upon the lateral surface of the adult brain. X 10. A probable direct connection 

 from the superior visceral-gustatory nucleus (nuc.i'is.ti.) to the hypothalamus is indicated by 

 the dotted line. 



Figtire 9. — Diagrammatic transverse section of the larval medulla oblongata near the level 

 of the IX nerve roots, showing four types of neurons of the sensory zone. X 100. Drawn 

 from preparations illustrated in 1914. Figure 89 shows a section of the adult brain in about 



