292 



From the precediüg descriptions of the several canals and foramina 

 that traverse the skull of Polyodon in the prootic region, it is evident 

 that there is no trigemino- facialis chamber in this fish comparable 

 to that found in Amia, Lepidosteus and certain teleosts. But that 

 chamber would apparently arise if the eyeball and the orbit of 

 Polyodon were to be enlarged so as to force the trigeminus foramen 

 backward until it should lie within the anterior opening of the 

 facialis canal; the latter opening then transmitting the trigeminus, 

 lateralis and abducens nerves, the jugular vein and the external carotid. 

 Close to or even within this opening, the oculomotorius would per- 

 forate the cranial wall, and the mesial wall of the chamber would 

 be perforated by the trigeminus and facialis nerves and by the internal 

 jugular vein. The internal carotid would run forward external to the 

 ascending process of the parasphenoid instead of internal to it, as in 

 Amia. But if the dense connective tissue that, in Polyodon, surrounds 

 and encloses the artery as it passes along the outer surface of the 

 ascending process of the parasphenoid were to ossify and become part 

 of that process, conditions would arise almost exactly similar to those 

 in Amia. Anterior to the process the artery perforates the basis 

 cranii, in Polyodon as in Amia, by a special internal carotid canal. 



Palais de Carnoles, Menton, France, April 2V^ 1911. 



Literature. 



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