661 



parietal and connected with suborbital canal in frontal; 3) the 

 operculo-mandibular canal piercing the lower jaw and praeoper- 

 culum, and joining the infraorbital canal near the hind endJ|of the 

 squamosal ; 4) the supratemporal cross-commissure travers- 

 ing the supratemporals (extrascapulas) and joining the infraorbital 

 canals. 



In Polypterus (Fig. 2) we have a similar arrangement, but] the 

 operculo-mandibular canal is not connected with the main-canal. |In 

 Trematosaurus (Fig. 3) of the Stegocephali we find the following 



Fig. 2. 



Fig. 3. 



Fig. 2. Polypterus bichir, Geofkk. 



n nasal. / frontal, p parietal, pro praeoperculum. stp supratemporalia. ptp post- 

 temporcal. 



Fig. 3. Trematosaurus braunii, Burm, (From H. v. Meyer.) 



pm praemasillary. n nasal. / frontal, p parietal, m maxillary, pr/r praefrontal. 

 p/r postfrontal, po postorbital, j jugal. qj quadratojugal. sq squamosal, psq pro- 

 squamosal. sopl supraoccipital plate (supratemporal Fishes), popl paroccipital plate (supra- 

 temporal Fishes). 



conditions. We can distinguish the infra- orbital, supra-orbital canal 

 and the supratemporal cross commissure, besides a fourth canal which 

 is found in the squamosal region and seems to correspond to the pre- 



