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Show 1904.] OSTEOLOGY OP THE ELOPID.E AND ALBULID.E. 49 remarkable that the pro-otic rises so high as to touch the frontal. The front part of the side of the basioccipital a,nd the lower part of the pro-otic are greatly inflated, much as in Osmerus. Incision into the bulla shows that it is for the accommodation of the very large sacculus, with otolith of equivalent size, and not for any diverticulum of the swim-bladder. The opisthotic is moderately small, and lies equally upon the exoccipital, epiotic, and squamosal; it sends no process forward to meet the pro-otic. The orbital surface of the alisphenoid is in a plane nearly transverse to the axis of the cranium. The basisphenoid has the form of a Y when seen from the front, but a thin plate of bone continues forward from the stem of the Y into the interorbital septum to meet the orbitosphenoid. The upper limb of the Y is attached on each side to the alisphenoid and pro-otic. The orbitosphenoid is largely developed, and, with the assistance of the basisphenoid, forms a complete osseous interorbital septum. The parasphenoid extends very nearly to the occipital articulation, and the eye-muscle canal opens posteriorly by a small aperture. The part of the parasphenoid lying below the orbital region bears numerous hemispherical teeth, disposed in a coffinshaped patch. Just where the front of the parasphenoid meets the back of the vomer is an oval space, which is roofed in by a forward continuation of the dorsal part of the parasphenoid. The vomer bears two or three transverse rows of pointed teeth. The ethmoid region of the cranium is long, the distance from the front of the mesethmoid to the back of the prefrontal being greater than the length of the orbit. The mesethmoid projects considerably in front of the vomer ; it has a trough on its upper surface instead of the more usual ridge, and below the trough has a foramen of elliptical shape, visible in a side view only. Temporal and Preopercular Series.-The post-temporal has three limbs. The largest lies over the epiotic, the second or deep one is more slender, and is attached by ligament to the back of the opisthotic, while the third one runs forward beneath the supratemporal and spreads out into osseous tendons, to which are attached fibres of the trapezius muscle, inserted into the posterior temporal vacuity. The supratemporal has a rather flat external surface, which is flush with the external surface of the squamosal. The transverse commissure of the sensory-canal system, after leaving the upper end of the supratemporal does not run in the parietal, but superficially to its posterior edge. The preopercular is bent at an angle of about 108 degrees, and the upper limb is-slightly longer than the horizontal limb. Circumorbital Series.-There are in all twelve bones of this series (text-fig. 16, p. 50). The most anterior ones are curious, basket-like bones, not much wider than the sensory canals which they carry. The canals in this region are particularly large. Maxillary Series.-The upper part of the premaxilla is sculptured into a spongy-looking basket-work similar to that of the naso-lachrymal bones. Unless the mouth is very widely opened, the P roc. Z ool. S o c-1904, V ol. II. No. IV. 4 |