FISHES OF FAMILY BLENNIIDAE 25 



pterosphenoid forms a synchondral joint with its respective sphenotic 

 along a ridge on the internal surface of the sphenotic. 



Basisphenoid (fig. 2). — Viewed dorsaUy, the median basisphenoid 

 appears Y-shaped with the broad arms ("meningost" — see discus- 

 sion under sphenoid region, p. 43) of the Y oriented posterolaterally 

 and the slender, pointed shank directed anteriorly. There is a foramen 

 present just anterior to the angle of junction of the arms of the Y (not 

 present in all specimens). The shank extends into the interorbital 

 septum, where it bends sharply ventraUy and just fails to reach the 

 dorsal surface of the parasphenoid. The distolateral margin of each 

 basisphenoid arm forms an overlapping, irregular joint with the 

 ventralmost internal surface of its respective pterosphenoid, thus 

 sandwiching this narrow pterosphenotic portion between the basi- 

 sphenoid and ascending process of the parasphenoid. For a short 

 distance ventral to its joint with the pterosphenoid, the ventral surface 

 of the distal margin of each basisphenoid arm rests on an internally 

 projecting surface of its respective ascending wing of the parasphenoid. 



The posterior muscles of each eye pass beneath the basisphenoid 

 and extend along the floor of the cranium (dorsal surfaces of the shank 

 of the parasphenoid and basioccipital) and terminate just anterior 

 to the ventral margin of the foramen magnum. Other than the roof 

 formed by the basisphenoid anteriorly, the muscles are not roofed by 

 bone (the roof of the posterior myodome is membranous for most of 

 its length). 



Prootic (figs. 1,2, 4). — ^Each complex prootic joins the parasphenoid 

 along the grooved prootic ventral and ventroposterior margins; joins 

 its respective sphenotic along the prootic dorsal margin, its respective 

 pterotic along the prootic dorsoposterior margin, its respective exoc- 

 cipital along the prootic ventroposterior margin, and the basioccipital 

 for a short distance at the prootic's internal ventroposteriormost 

 margin. Dorso-anteriorly, each prootic overlaps the posterior margin 

 of its respective pterosphenoid and forms a joint with the pterosphe- 

 noid's posterior margin along the prootic's internal dorso-anterior 

 margin. On the dorsoposterior external surface, each prootic is over- 

 lapped by its respective intercalar. Variably, a shallow pocket may 

 be present on the external surface of the prootic into which a narrow 

 portion of the edge of the intercalar may insert. On its external surface 

 each prootic bears a bridge that ends dorsally at the ventral portion 

 of a fossa in which the anterior condyle of the hyomandibular artic- 

 ulates (the dorsal portion of the fossa is formed by the sphenotic). 

 Internal to the bridge is a hoUow with a large opening to the interior 

 of the cranium. A second smaller opening exists at the posteroventral 

 origin of the bridge. The trigemino-facial complex of nerves passes 



