No. i.] MORPHOLOGY OF THE PETROSAL BONE. 19 



lateral chamber of the eye-muscle canal, the profundus gan- 

 glion in the orbital opening of that chamber. The ganglia 

 are therefore both intradural in position, as the trigeminal 

 ganglion is in man (No. 24, vol. iii, pt. ii, p. 234). The 

 trigemino-facial ganglion lies in Amia immediately in front of 

 the anterior bounding wall of the labyrinth recess and would 

 lie on the dorsal surface of that wall if the hind end of the 

 skull were flexed downward as it is in man. The anterior wall 

 of the labyrinth recess is partly ossified as the petrosal. The 

 upper, lateral chamber of the eye-muscle canal of Amia is thus 

 both functionally and in position the equivalent, if not the 

 homologue, of the cavum Meckelii of man. 



In teleosts the Wurzelganglien dcs Trigeminus lie, according 

 to Sagemehl (No. 26, p. 463), in the fatty portion of the dura 

 mater, between the outer and inner limiting membranes of that 

 structure. If the ganglia so defined form or belong to the Gas- 

 serian ganglion, that ganglion in teleosts occupies a position 

 markedly different from what I find in Amia. 



In other fishes parts of the trigemino-facial ganglionic com- 

 plex may lie in canals in the side wall of the skull, and parts of 

 it entirely outside the skull, as in Chimaera (No. 9), Laemargus 

 (No. 10), and Acipenser (No. 12). In Necturus (No. 17) the 

 several ganglia lie entirely outside the skull. Whether in 

 these several cases, and in other similar ones, the ganglia 

 are morphologically different in position from what they are 

 in Amia, or not, depends entirely upon the positions of the 

 two layers of the dura mater, and not upon the relations 

 of the ganglia to the side walls of the skull. Unfortunately, 

 the relations of the dura mater and its different layers to the 

 ganglia are not given in any of the descriptions that I find. 



The internal auditory meatus, the internal orifice of the 

 canal by which the facial nerve in man leaves the cranial 

 cavity, lies, according to Thane (No. 24, vol. ii, pt. i, p. 75), 

 between the prootic and opisthotic portions of the petrous 

 portion of the temporal bone. The prootic lies above the 

 meatus, the opisthotic below it. The facialis in man, in that 

 part of its course that traverses the side wall of the primordial 

 cranium, cannot accordingly be considered as lying, in any 



