THE BRAIN OF RHINOCHIMAERA. 



By BURT G. WILDER. 



(Read April 23, 1908.) 



Four years ago, to the small but very peculiar and ancient group 

 of shark-like fishes known as Chimeroids, Holocephala and Chis- 

 mopnea, Garman added a Japanese species, Rhinochimaera pacifica. 

 His description of the brain was brief and the figures represented 

 only the general form from the dorsum, venter and side. A well- 

 preserved example recently obtained from Alan Owston of Yoko- 

 hama enables me to confirm Carman's account as to the general 

 Chimeroid character of the brain, especially the cerebellum and 

 adjoining segments, and as to the extraordinary — probably unique — 

 slendemess of the other regions, due not merely, as in Chimaera, 

 to the elongation of the cerebral crura, but also to the pedunculate 

 condition of the olfactory bulbs, whose tracts or crura equal the 

 cerebral in length. The partial dissection of this brain discloses 

 additional features, as shown upon the colored crayon diagram, viz., 

 (i) The cerebral and olfactory cavities. (2) The complete circum- 

 scription of these cavities by walls of moderate thickness at the olfac- 

 tory bulbs and parts of the cerebral hemispheres, but mostly thin 

 and largely membranous. (3) The olfactory crura have thinner 

 walls than in any brain known to me, and the proper nervous sub- 

 stance seems to be confined to their outer or lateral sides. (4) The 

 roof of the undivided cerebral cavity is wholly membranous ; like- 

 wise a narrow mesal zone of the floor, but the floors df the hemi- 

 spheres are connected by a terma (" lamina terminalis ") as described 

 by me in Chimaera in 1877. (5) Each substantial wall of the cere- 

 bral cavity begins as a single broad band which divides into a ventral 

 and a lateral portion as it approaches the hemisphere ; this condition 

 has not been observed by me in any other brain. (6) There was 

 found no trace of the Nervus terminalis of Locy ; nor has it been 

 recognized in any other member of the group. 



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