172 



NERVOUS SYSTEM OF VERTEBRATES. 



part of the cerebellum which projects into and largely fills up the 

 ventricle of the mesencephalon, — the valvula cerebelli. In selach- 

 ians no valvula is present. The cerebellum corresponds to that 

 part of the cerebellum of bony fishes which is folded upward and 

 outward. This will be clear from a comparison of Fig. 91, which 

 represents a sagittal section of the cerebellum of a newly hatched 

 bony fish, with Fig. 11, representing a sagittal section of a selachian 

 brain. The superior secondary gustatory nuclei in selachians 

 are situated higher in the dorso-lateral wall of the metencephalon 

 than in bony fishes and their commissure crosses in the roof of 



/o/jas I/// 

 lobus IX 

 lob us X 



nor 10 



Fig. 90. — A diagram of the gustatory paths in the brain of the carp as seen from 

 the left side. From C. Judson Herrick. 



n.VII.s., n.IX.s., and n.X.s., represent the sensory root fibers of the facialis, 

 glossopharyngeus and vagus respectively, or gustatory neurones of the first order 

 (/). The secondar)^ tracts, both ascending and descending, are marked II. The 

 tertiary path to the inferior lobe is marked III; the path to the cerebellum and 

 valvula, Hi. The return path from the inferior lobe to the motor nuclei of the 

 oblongata (tractus lobo-bulbaris) is marked IV. The commissures of the inferior 

 and superior secondary nuclei are indicated by shaded areas (the latter marked c). 

 n.op., the optic nerve. The area marked 71. fun. includes the funicular nucleus and 

 the inferior secondary gustatory nucleus. 



the brain at the junction of the tectum opticum and cerebellum. 

 This commissure has been described in selachians and amphibia 

 as the decussation of the velum medullare anterius. It is ob\-ious 

 that it is homologous with the inferior cerebellar commissure 

 which passes through the valvula of bony fishes. Hence it must 



