294 THE BRAIN OF THE TIGER SALAMANDER 



tissue which is the primordium of the floccular part of the mam- 

 mahan flocculonodular lobe. 



Commu-sura infima Halleri. — This is a decussation of the fascicuH 

 soHtarii at the calamus scriptorius, containing both root fibers and 

 secondary fibers of the visceral-gustatory system and doubtless also 

 commissural fibers between the two commissural nuclei of this sys- 

 tem. 



Commifisure of the funieular nuclei. — Intimately associated with 

 the preceding are commissural fibers between the nuclei of the dorsal 

 funiculi in the calamus region, with which decussating fibers are 

 mingled. This dorsal commissure of somatic sensory fibers is ex- 

 tended, reduced in size, downward through the entire length of the 

 spinal cord. There is some evidence that the visceral sensory com. 

 infima is also represented in the cord (p. 125). 



This completes the summary of the dorsal commissures. We now 

 turn to the ventral series, beginning, as before, at its anterior end. 



THE VENTRAL COMMISSURES 

 COMMISSURA ANTERIOR 



The complex com. anterior occupies the entire anterior commissure 

 ridge except its dorsal border. Its largest components are the partial 

 decussations of the medial forebrain bundles below and the lateral 

 forebrain bundles above (figs. 25-28). Associated with these fibers 

 are others, including the com. amygdalarum (which is part of the 

 stria terminalis system, p. 256), some fascicles of the nervus ter- 

 minalis, and a dispersed decussation between the olfactory fields of 

 the anterior parts of the hemispheres ('396, fig. 21). 



The crossing fibers of the anterior commissure ridge are enveloped 

 by a thin layer of gray which expands laterally as the large bed- 

 nuclei of the anterior commissure. The thin floor of the long preoptic 

 recess between the anterior commissure ridge and the chiasma ridge 

 contains the longitudinal fibers of tr. preopticus, some of which 

 decussate here. 



CHIASMA OPTICUM 



All fibers of the optic nerves decussate in the chiasma opticum. 

 The crossing occupies the anterior border of the chiasma ridge (figs. 

 2B and 2C). At the posterior border of the chiasma there is some 

 mingling of optic fibers with those of the postoptic commissure, but 

 in some of our Golgi preparations the optic fibers are electively im- 

 pregnated and can be separated from the others ('41, '42). 



