GREGORY: FISH SKULLS 391 



following factors: (1) marked depression of the quadrate-articular joint; (2) the retraction 

 of the upper border of the mouth by shortening of the preorbital region. 



The dorsal position of the mouth and the unusually large size of the ascending and 

 articular processes of the premaxillae, together with other factors to be noted below, have 

 caused a deep V-shaped notching of the anterior median portion of the frontals and a sharp 

 depression of the mesethmoid, which in the lateral aspect forms a narrow curved bar with 

 an expanded lower end resting on the parasphenoid and vomer; the main bar lies behind and 

 below the level of the everted orbital wings of the frontal; it runs backward and upward to 

 the depressed median portion of the frontals. This V-shaped dorsal fossa is bridged in front 

 by the transversely extended vomer, which forms the keystone of the large premaxillo- 

 maxillary arch. Thus the strange characters of the forepart of the skull, as figured by 

 Starks (1926a, pp. 320, 321) and by Regan (1912/) are fully explicable as part of the primary 

 adaptive habitus of the pediculate mouth and jaws. 



As the orbits are pushed backward so that they impinge upon the suspensorium, it is 

 natural that the roof of the cranial vault should be short and wide. The supraocclpital 

 has retained its acanthopterygian contact with the frontals; the middle of it cooperates 

 with them to form a flat-bottomed valley that widens in front; toward the deepest part of 

 this depression point the anterior end of the bony rod that supports the third dorsal ray 

 and the posterior end of the bony rod of the second dorsal fin-ray. (The illicial ray and its 

 short bony support rest in the skin above the ascending processes of the premaxillae.) 

 Various parts of the skull roof, in other cases, have readily moved forward and expanded 

 laterally under the influence of cephalic extensions of the dorsal fin (e.g., in the echeneids, in 

 Coryphcsna, Luvarus). Thus the enlargement of the basal muscles of the second and third 

 rays of the spinous dorsal may have initiated the enlargement of the supraocclpital, which 

 even here is already the dominant median element of the cranial vault. As the supra- 

 occipital has moved forward the epiotics have followed it, drawing in toward the mid-line 

 but not quite meeting there except in front. The parietals have retained their primitive 

 percoid positions, being separated by the supraocclpital. In my specimens they are repre- 

 sented by thin plates in front of the lunate epiotics and lateral to the supraocclpital; laterally 

 they overlap the sphenotics and the pterotics. These two stoutly-braced elements have 

 sharply projecting postorbital and posthyomandibular processes separated by a deep notch. 

 This bears beneath its dorsal rim the usual facets for the anterior and posterior heads of the 

 hyomandibular. All this region that receives the upward thrust of the suspensorium is 

 strengthened by various trabecular tracts and crests on the lateral surface of the prootic, 

 pterotic and exoccipital. A triradiate suture connects the sphenotic, prootic and pterotic, 

 while another triradiate suture marks the contact of exoccipital, pterotic and epiotic. 

 The posttemporal is a much shortened and broadened, more or less triangular bone which 

 suspends the long pectoral girdle and is closely tied to the back of the epiotic, pterotic and 

 exoccipital. 



Inasmuch as the very long suspensorium and the long shoulder-girdle apply powerful 

 forces to the back part of the cranial vault, the occiput is reinforced by the enlarged first 

 vertebra, which has become almost immovably attached to it. However, the triple occipital 

 condyle, which is characteristic of percomorph fishes, still marks the posterior limits of the 

 skull proper. The stoutly-built centrum of the first vertebra articulates with the basiocci- 

 pital by the usual subcircular cotylus but its posterior face forms a much widened, almost 



