— 172 — 



The FRONTAL is an eight-sided bone, each side being straight or slightly concave. One 

 of these sides forms the middle portion of the dorsal margin of the orbit, another suturates with the 

 frontal of the opposite side, the others suturating with the ectethmoid, nasal, supraoccipital, parietal, 

 pterotic and postfrontal. The bone has no ventral flange. It rests upon the expanded dorsal edges 

 of the bodv and brace-like internal process of the alisphenoid, on a small portion of the sphenotic, 

 and on a small projecting shelf from the deeper layers of the anterior edge of the supraoccipital. It 

 is traversed by the supraorbital latero-sensory canal and lodges five organs of the line, as will be 

 later fully described. 



The POSTFRONTAL is a small dermal bone that lies upon and is inseparably fused, in all 

 of my adult specimens, with a lateral portion of the dorsal surface of the sphenotic. It suturates 

 with the frontal and dermo -pterotic, and is traversed by the main infraorbital latero-sensory canal, 

 lodging one organ of that canal, innervated by the oticus lateralis. 



The PARIETAL is a sub-oval bone, bounded anteriorly by the frontal, laterally by the 

 pterotic, posteriorly by the lateral and mesial extrascapulars, and mesially by the supraoccipital. 

 It rests upon the dorsal surface of the epiotic, upon the dorsal edges of those flanges of the proötic 

 and supraoccipital that form the antero-mesial wall of the labyrinth recess, and also upon a small 

 shelf projecting mesiallv from what are apparently the deeper layers of the dermal portion of the 

 pterotic. 



The LATERAL EXTRASCAPULAR is a small oval bone traversed by the lateral portion of 

 the supratemporal commissure of the latero-sensory canals, and lodging one organ of that canal. 

 It is not traversed by the main infraorbital canal, but a groove on its lateral edge lodges a short 

 section of that canal, apparently without related organ, as will be further explained when describing 

 the canals. It is bounded antero-mesially by the parietal, antero-laterally by the pterotic, postero- 

 laterally by the suprascapular, and postero-mesially by the mesial extrascapular. It has no bounding 

 relations either to the subtemporal fossa or to the large fossa on the posterior surface of the skull, 

 its ventral surface being entirely covered by the epiotic, pterotic and suprascapular, on which bones 

 it rests. 



The MESIAL EXTRASCAPULAR is a large subrectangular bone with straight and nearly 

 parallel lateral and mesial edges. It is traversed by the mesial section of the supratemporal com- 

 missure and lodges one organ of that commissure. It suturates, in the middle line, with its fellow 

 of the opposite side. Anteriorly, it is bounded by the supraoccipital and parietal, and laterally by 

 the lateral extrascapular and suprascapular. Its mesial third, approximately, lies upon the broad 

 flat dorsal surface of the Spina occipitalis, its lateral third resting upon a shelf-like portion of the 

 mesial edge of the suprascapular. Between those two bones it forms part of the roof of the large 

 fossa on the corresponding side of the posterior surface of the skull. 



The SUPRASCAPULAR is a large bone with a prolonged and pointed bind end. It is bounded 

 anteriorly by the pterotic, antero-mesially by the lateral extrascapular, and mesially, along the 

 anterior half only of its length, by the mesial extrascapular. The lateral half of the bone is bent 

 downward at an angle to the mesial portion, as already stated, and along this angle there is a stout 

 ridge which begins at the anterior quarter of the bone and extends back ward to its pointed bind end. 

 The bone is traversed by the main infraorbital latero-sensory canal and lodges one organ of that line, 

 innervated by a branch of the supratemporalis lateralis vagi. This organ, in 5 cm specimens, is much 



