OCR Text |
Show 1904.] OSTEOLOGY OP CLUPEOID FISHES. 473 encloses a vesicle of the swim-bladder, the pre-epiotic fossa above it is rendered very shallow as compared with that of Clupea. The auditory fenestra, opening into the perilymphatic cavity, is bounded by the pro-otic, exoccipital, and basioccipital, as in Clupea. Text-fig. 133. Cranium of Engraulis encrasicholus, left side. For explanation of lettering see p. 493. The foramen for the trigeminal nerve is of large size ; it faces more anteriorly than usual, and is bounded by the alisphenoid and pro-otic, instead of by the pro-otic alone. The pro-otic bulla, like that of the squamosal, is large; it is not spherical, but is drawn out in a direction nearly at right-angles to the median plane of the head (see Journ. Anat. and Phys. xxvi. 1891, p. 36, and p. 32, fig. D). A basisphenoid is present, but it has no descending limb. The articulation for the hyomandibular is situated rather far forward ; the anterior head of the hyomandibular articulates with the postfrontal, and the hinder with the squamosal. The lateral temporal groove is broad and shallow. Removal of its floor exposes a fairly large cavity opening laterally by two apertures-one over the articular process of the squamosal for the reception of the posterior head of the hyomandibular, and the other immediately in front of this. The cavity is roofed by the frontal, and is bounded in front by the postfrontal, behind by the squamosal, and below mainly by the pro-otic. The parasphenoid is depressed at about the middle of its length, doubtless in relation with the large size of the eyes. It does not project behind the occipital articulation, but it ends posteriorly in a pair of parallel lamellae on the right and left sides of the posterior outlet of the eye-muscle canal. Both parasphenoid and vomer are edentulous. The front of the cranium is formed by the mesethmoid, and not by the vomer (cf. Clupea). The mesethmoid is large, of considerable vertical extent, but thin; the prefrontals are relatively small. The orbitosphenoid is small, and |