— 147 — 



The cavum sinus imparis extends, in Peristedion, but slightly beyond the middle of the length 

 of the basioccipital, the bone posterior to it having a relatively broad, concave dorsal surface, the 

 posterior portion of which forms the ventral boundary of the foramen inagnum and the floor of the 

 cranial cavity immediately anterior to that foramen. Lateral to the cavum sinus imparis the bone 

 lodges a small portion of the short subcircular saccular groove. 



The basioccipital is, as usual, bounded dorsally, on either side, by the exoccipital, and anteriorly 

 by the proötic. Ventrally it is overlapped externally by the parasphcnoid. 



The EXOCCIPITAL is bounded by the basioccipital, proötic, pterotic, opisthotic, epiotic 

 and supraoccipital, and it is perforated by separate foramina for the glossopharyngeus, vagus and 

 occipital nerves. The vagus and occipital foramina have positions sirailar to those in Trigla, the 

 vagus foramen, in all niy specimens, being divided into two parts by a transverse bar of bone. The 

 glossopharyngeus foramen lies directly anterior to the vagus foramen, at one half or two thirds the 

 distance to the anterior edge of the bone. Immediately dorsal to the vagus and glossopharyngeus 

 foramina there is a slight horizontal ridge along the outer surface of the bone; and dorsal to this 

 ridge, nearly the entire lateral surface of the brain case is occupied by a large subtemporal depression 

 which, as in the other fishes of the group, gives origin to the adductor hyomandibularis and adductor 

 operculi muscles, and probably also to the fourth and fifth levators of the branchial arches; but the 

 origins of the levator muscles of the branchial arches were not investigated. The fossa on the proötic, 

 so well developed in Scorpaena, is apparently represented, in Peristedion, by a slight groove along 

 the anterior edge of the subtemporal depression. 



On the internal surface of the exoccipital there is a mesial process, but it has almost completely 

 coalesced with the lateral wall of the bone, thus here giving to the bone a thick and distinctly double 

 ventral edge which suturates with the basioccipital. At the anterior end of this thick ventral edge, 

 the mesial process separates slightly from the side wall of the bone and so bounds a small dorso- 

 posterior portion of the saccular groove. 



The OPISTHOTIC forms part of the thin ventro-laterally projecting portion of the postero- 

 lateral edge of the skull. It lies in a nearly transverse position, filling a large and somewhat square 

 interval between the ventral edge of the posterior process of the pterotic and a right-angled incisure 

 in that portion of the exoccipital that forms part of the postero-lateral edge of the skull. Because 

 of its nearly transverse position, the bone forms part of the flat posterior surface of the skull. A 

 process on its postero-mesial surface gives articulation to the opisthotic process of the suprascapular, 

 suturating with it. The antero-mesial edge of the bone expands, Y-shaped, and overlaps externally 

 the adjoining edges of the pterotic, exoccipital, and epiotic, covering also an interval of cartilage 

 between those bones. The interval of cartilage forms part of the wall of that recess of the cranial 

 cavity that lodges the bind end of the sinus posterior utriculi and the related ampuUa posterior, 

 and if the cartilage were to be suppressed the opisthotic would form part of the bounding wall of 

 the recess. 



The EPIOTIC is normal. 



The PTEROTIC is bounded, in its deeper, primary portion, by the sphenotic, proötic, 

 exoccipital and epiotic, the opisthotic overlapping, externally, the ventral edge of that part of the 

 pterotic that encloses the posterior portion of the external semicircular canal. The dermal portion 

 of the bone is bounded by the frontal, postfrontal, parieto-extrascapular, lateral extrascapular and 



