— 167 — 



portion in that long and wide space that lies between those surfaces of the proötics of eitlier side 

 that suturate with the lateral edges of the parasphenoid, while in its anterior portion it i.s 

 represented in the space that lies between and anterior to the orbital portions of the proötics, 

 this space opening onto the floor of the myodome and being filled by the transverse ridge on the 

 dorsal surface of the parasphenoid. This latter ridge on the parasphenoid is accordingly the greatly 

 shortened and widened homologue of the longitudinal ridge on the bone in the other fishes of the 

 group. A result of this arrangement is that the pituitary opening of the brain case is partly filled, 

 toward the orbit, by the transverse ridge on the parasphenoid, and that the hind end of the pituitary 

 opening is confluent with the hypophysial fenestra at the hind end of that portion of the fenestra 

 that opens onto the floor of the myodome. 



The lateral surface of the proötic has dorsal and ventral regions separated by a pronounced 

 but rounded angle which starts from the dorsal edge of the trigemino-facialis chamber and runs 

 postero-mesially to the hind edge of the bone. The dorsal portion of the surface forms the anterior 

 portion of a large subtemporal fossa, described below. On the internal surface of the bone, and 

 parallel with this dorsal portion of its lateral surface, there is a tall f lange of bone which projects 

 from below upward and forms the anterior wall of the labyrinth recess. The dorsal edge of this flange 

 is partly capped with cartilage and there gives support to the hind edge of the frontal and to the 

 parietal, the hind edge of the flange projecting postero-mesially beneath the supraoccipital and there 

 being continuous with a slight ridge on the internal surface of that bone. The deep tall space between 

 the flange and the lateral wall of the bone is continued dorso-antero-laterally by a slight recess on the 

 internal surface of the sphenotic, and the large recess thus formed between the two bones lodges 

 not only the anterior semicircular canal and the anterior portion of the utriculus, but probably also 

 the anterior end of the sacculus, for there is no differentiated saccular groove. The recess must 

 also lodge an anterior portion of the external semicircular canal. for that canal leaves the recess 

 near its dorso-antero-lateral corner to enter it own special canal in the pterotic. The exact relations 

 could not be determined because of the want of sufficient material. 



Anteriorly the proötic is bounded by, and is partly in synchondrosis and partly in sutural 

 connection with the alisphenoid. Dorsally and posteriorly it is in similar relations with the sphenotic, 

 pterotic, basioccipital and exoccipital. Ventrally it is overlapped externally by and is suturally 

 connected with the parasphenoid. 



The PTEROTIC has, more than in the other fishes of the group, the appearance of being 

 formed of two separate and independent components secondarily fused with each other, for, although 

 the two components have the same length, they are not exactly superimposed; the dermal component 

 projecting forward beyond the primary component, and this latter component projecting posteriorly 

 beyond the dermal one. This projecting portion of the primary component supports the anterior 

 edge of the suprascapular. 



The dermal component of the bone is bounded, as usual, by the frontal, postfrontal, parietal, 

 lateral extrascapular (rocher) and suprascapular, and the lateral half of this part of the bone is bent 

 abruptly downward, as are also corresponding portions of the postfrontal and suprascapular, a rounded 

 longitudinal angle thus being formed, which extends across the three bones and terminates, at ich 

 hind end of the suprascapular, in a strong spine. This component of the pterotic is thus an angular 

 bone placed longitudinally along the lateral edge of the dorsal surface of the skull. It is traversed 

 by the main infraorbital latero-sensory canal and lodges three sense organs of that line, two innervated 



