292 Dr. Hancock on the Composition of the Fin Rays 



^ jgiriJmoiH .i308SictJLA on the Brain. ij^ i«wMsi%^tf ^aV 



I also alluded, in the last number of this Journal (p. 134), 

 to those petrous or bony appendages found within the cavity 

 of the cranium, and in contact with the brain, in the gilbagre 

 and other fishes — the siluri, more especially, of the Guiana 

 coast tiicnl d^i}m ^sh/i* m(^^'VV)^-*i.^ -'n^nu') 



These petrous bodies, from their situation, I had denominated' 

 brain-bones, being uncertain whether or not they might pertain 

 to the auditory organ. After having, in Guiana, consulted the 

 writings of Buffon and Daubenton, the only ones which pre- 

 sented on the subject, I perceived nothing to identify them 

 with the organ of hearing. The observations of Blumenbach, 

 which I have subsequently had access to in London, liave very 

 little contributed to remove the obscurity. '-n .(/ff^rrihd: ' 



I shall here transcribe the only passage that appears at all 

 to bear on the present subject, from Blumenbach's Manual of 

 Comparative Anatomy, translated by Laurence, revised and 

 corrected by Coulson, 1827 : — " It is only in some genera of 

 cartilaginous fishes, viz., the skate, shark, and lampreys, that 

 a tubular appendix of the vestibulum is continued backwards 

 and outwards, so as to represent a rudiment of a tympanum." 



" Much light has lately been thrown on the organ of hearing 

 in bony fishes, by Professor Weber. They possess near the 

 anterior cervical vertehrce considerable ossicula, which may be 

 compared to the malleus, incus, and stapes; and, in those 

 which are provided with a swimming-bladder, these bones are 

 so connected with that organ as to render it probable that it is 

 auxiliary to the sense of hearing.? " 



*' Their internal ear consists of three large canals, which are 

 generally seen to project into the cavity of the cranium. Op- 

 posite to the termination of the auditory nerves on the ves^ 

 tibulunij one, two, or three, neatly-formed stones are found. 

 These are white as porcelain, particularly in several of the 

 bony fishes, ^nd y.ery dry and brittle ia their texture."-^ 

 P. 28^.iroiiK»qotq in isfssaltnsi «/9ili ^?.9n^'ido loivuD .M h 



Here is nothing said respecting bones posited in the cavity 

 of the skull, and in contact with the hemispheres of the brain i 



