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with the corresponding, or trigeminal part of the ramus ophthalmicus 

 of Petromyzon. The lateralis component of this nerve, in Bdellostoma, 

 and also that of Trigeminus II are found as distinct and important 

 branches of their respective nerves. 



The Skull and Pharyngeal Basket. 



The primordial membranous cranium of all vertebrates possesses, 

 inherently, the possibility of chondrification ; but it possesses also the 

 possibility of remaining membranous. While these two statements 

 might be considered axiomatic, they are not always both sufficiently 

 borne in mind. 



In the preceding pages it has been shown that the several 

 branches of the n. trigeminus and n. facialis all issue from a chamber 

 that forms a part of the membranous cranium. In lodging and trans- 

 mitting these nerves, and also in its general position in relation to 

 the cranium, this membranous chamber of Bdellostoma resembles the 

 upper lateral chamber of the eye-muscle canal of Amia. That chamber 

 of Amia (2, Fig. 11) is separated from the main, ventral portion of 

 the eye-muscle canal by a projecting ridge of cartilage, the anterior 

 end of which supports the pedicle of the alisphenoid and then con- 

 nects with the lateral end of the transverse, basisphenoidal "Wulst" 

 of Sagemehl's (27) and my own descriptions. The several branches 

 of the trigeminus and facialis nerves of Amia, excepting only the 

 ramus palatinus facialis, all issue from the upper lateral chamber by 

 foramina that lie dorsal or lateral to this ridge. The palatinus facialis 

 first runs downward mesial to the ridge, and then pierces the lateral 

 wall of the main eye-muscle canal ventral to the ridge. In Bdello- 

 stoma, this ridge of Amia is represented, in its relations to the nerves, 

 by the so-called palatine and trabecular bars considered as a single 

 continuous cartilage; for the so-called fenestrae that transmit the 

 maxillo-mandibularis trigemini and facialis nerves lie lateral to the 

 trabecula, while the palatinus posterior trigemini, which apparently 

 replaces the palatinus posterior facialis of Amia, runs downward mesial 

 to the hind end of the palatine. The anterior end of this palato- 

 trabecular bar turns mesially to form a transverse commissure which 

 bounds anteriorly the large hypophysial fontanelle of the fish, exactly 

 as the transverse basisphenoidal bar, in Amia, bounds anteriorly the 

 smaller hypophysial fenestra of that fish. The transverse commissure 

 of Bdellostoma has, however, not at all the same relations to the over- 

 lying parts of the brain that the basisphenoidal bar of Amia has, 

 those relations being much more nearly presented by the bar tr of 



