144 Edward Phelps Allis jr.. 



arising: from the summits of small bony processes of the cranium. 

 The dorso -posterior process is much stronger and often much longer 

 than the anterior one. The side wall of the skull from which these 

 processes arise is entirely of bone, and is formed of what is probably 

 the frontal part of a massive fronto-sphenoid bone, a bone apparently 

 formed by the complete fusion of the frontal with the orbitosphenoid. 

 The main infraorbital canal turns backward, ventral to the base of 

 the posterior of these two processes, and immediately enters a canal 

 which lies between the anterior end of a long anterior process of the 

 squamosal, externally, and the frontal internally. Between the bases 

 of the two fronto-sphenoid processes the infraorbital and supraorbital 

 canals anastomose, a posterior pouch-like extension of the supraorbital 

 canal running backward dorso-megial to the base of the posterior 

 process. Having entered the canal between the squamosal and frontal, 

 the main infraorbital canal runs backward and laterally in a nearly 

 straight line and soon becomes entirely enclosed in the squamosal, 

 which 4t traverses almost to its hind end. There it issues on the 

 dorsal surface of the bone and continues its course in that position 

 to the hind edge of the bone, the hind edge of the bone forming 

 part of the hind edge of the skull. The canal then makes a sharp 

 turn laterally and enters and traverses a short bony tube which lies 

 almost directly ventral to and parallel to the lateral end of the supra- 

 temporal commissure. Leaving this tube the canal immediately pierces 

 the anterior wall of, and thus communicates directly with, the trans- 

 verse canal here formed by the united supratemporal cross-commissure 

 and preoperculo-mandibular canal. 



In a part of its course through the squamosal the canal lies 

 immediately dorsal to and close to the horizontal canal of the ear. 

 In my young specimens the infraorbital canal here lies in a canal 

 formed externally by a lamina of perichondrial or dermal bone, 

 whichever it may be, and internally by the cartilage of the skull, the 

 membranous lateral sensory canal here lying directly upon the carti- 

 age. "l'he horizontal canal of the ear lies immediately ventral to it, 

 enclosed in a delicate ring of bone which is apparently of the same 

 character and origin as the bone enclosing the lateral sensory canal; 



