. Bulletin of the British Museum (Natural History). 268 P. H. GREENWOOD (Text-fig. 33). Since part of the dilatator operculi in clupeoids originates in this area, the muscle in Denticeps may be its homologue. The absence (or great reduction) of the dilatator operculi in Denticeps may be correlated with the shape of the greatly enlarged pterotic and the resulting position of the lateral-line openings into the recessus lateralis. If a dilatator was present it could only lie across these openings (Text-fig. 33). In the clupeoids examined (Text-fig. 34), despite their varied skull forms, the reces
. Bulletin of the British Museum (Natural History). 268 P. H. GREENWOOD (Text-fig. 33). Since part of the dilatator operculi in clupeoids originates in this area, the muscle in Denticeps may be its homologue. The absence (or great reduction) of the dilatator operculi in Denticeps may be correlated with the shape of the greatly enlarged pterotic and the resulting position of the lateral-line openings into the recessus lateralis. If a dilatator was present it could only lie across these openings (Text-fig. 33). In the clupeoids examined (Text-fig. 34), despite their varied skull forms, the recessus openings are so situated LAP u. Fig. 34. Clupea harengus. Jaw musculature (for abbreviations see Fig. 33). The head of the adductor mandibulae series has been dissected away to show the superficial inser- tion of the levator arcus palatini muscle. H: Hyomandibula; HRi: ridge on hyomandibula. as to lie above the muscle, whose upper margin skirts the lower lip of the foramina. (Parenthetically it may be noted that a dilatator fossa is present in the clupeoids, but not in Denticeps.) There are other myological differences, but these will not be discussed here. They do, however, reinforce the impression gained from those differences discussed above, namely, that compared with clupeoids, the orobranchial musculature of Denticeps is in part highly speciahzed, and in part much more primitive. Thus, for the moment it is impossible to classify the system in Denticeps as more or less primitive than the clupeoid condition. A similar conclusion is reached when the hyobranchial skeleton is considered. In its gross morphology, the branchial skeleton lacks the typical elongation of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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