17(5 THE BRAIN OF THE TIGER SALAMANDER 



The tr. tecto-cerebellaris was originally described ('*25, p. 483 and 

 figs. 39-41) from two series of sagittal Golgi sections of the adult, 

 and this description has been confirmed by Larsell ('3'2, p. 425). Ad- 

 ditional details can now be added. In several series of Golgi sections 

 of advanced larvae and adults these thin unmyelinated fibers arise 

 from neurons of the nucleus posterior tecti with the dendrites direct- 

 ed forward into the posterior border of the optic tectum. Their axons 

 form a rather compact fascicle close to the dorsal surface of the nu- 

 cleus posterior, which passes backward though the anterior medul- 

 lary velum and laterally of it, accompanying thick myelinated fibers 

 of the mesencephalic root of the V nerve which take a similar course. 

 At the anterior border of the cerebellum they turn ventrad and 

 spread out along the anterior side of the body of the cerebellum, 

 some reaching the underlying nucleus cerebelli. 



A tr. mamillo-cerebellaris was described by Larsell ('20, p. 279; 

 '32, p. 424), and some evidence of it has been seen in our prepara- 

 tions; but in the absence of elective impregnations no satisfactory 

 description can be given. In view of the large size of this connection 

 in fishes, its presence in urodeles may be expected. 



BRACHIUM CONJUNCTIVUM 



Large numbers of unmyelinated and lightly myelinated fibers de- 

 scend from the body of the cerebellum, the auricle, and the nucleus 

 cerebelli. These cerebello-tegmental fibers are in addition to the con- 

 nections of the auricle with the vestibulo-lateralis sensory field in 

 correlation tracts a and b; they are directed in dispersed arrange- 

 ment ventrally, posteriorly, and anteriorly. A large and rather com- 

 pact fascicle of these fibers, a few of them myelinated, is directed 

 antero ventrally and is clearly a primordial brachium conjunctivum 

 (figs. 10, 21, 71). These axons arise from cells of the body of the cere- 

 bellum (fig. 47) and the nucleus cerebelli (14a, fig. 52); they assem- 

 ble anteriorly of the body of the cerebellum and pass forward through 

 the visceral-gustatory nucleus in the isthmus (figs. 33, 34). Here they 

 are joined by fibers of the tertiary visceral tract, which arises in 

 this nucleus (p. 169). 



This mixed tract with accessions of fibers from other sources has 

 been termed "fasciculus tegmentalis profundus" ('36, p. 304, figs. 14, 

 23, f.teg.p.) ; its analysis is possible only with the aid of elective im- 

 pregnations, and these, fortunately, are available (see the further de- 



