A treatise on zoology . -two large lateral plates (dermal-lateral ethmoid of Bridge),outside which lie the postfrontal and the squamosal. The latterbone, Avith the lateral and the occipital, forms a roof over the 240 DIPNOI jaw muscles. Now this squamosal is generally likened to that ofthe Amphibia, to which it bears a remarkable resemblance. Since,-in Ceratodus sturii (Teller [433]), it harbours the postorbital sensorycanal, it is probably the homologue of the pterotic (squamosal) ofthe hyostylic fishes. As it spreads downwards OAer the quadrateit appears to be a prespiracular bone, and there
A treatise on zoology . -two large lateral plates (dermal-lateral ethmoid of Bridge),outside which lie the postfrontal and the squamosal. The latterbone, Avith the lateral and the occipital, forms a roof over the 240 DIPNOI jaw muscles. Now this squamosal is generally likened to that ofthe Amphibia, to which it bears a remarkable resemblance. Since,-in Ceratodus sturii (Teller [433]), it harbours the postorbital sensorycanal, it is probably the homologue of the pterotic (squamosal) ofthe hyostylic fishes. As it spreads downwards OAer the quadrateit appears to be a prespiracular bone, and therefore can hardlyi^epresent, as has been suggested, the jjreopercular of other Osteich-thyes. For, in these, the hyomandibular sensory canal, supplied bythe post-spiracular hyomandibular Ijranch of the seventh nerve, islodged in the preopercular. In fact, a true preopercular has never Restoration of the liead of Ctowchi?. rn, maxilla ; pm, ])ieiiiaxillettiTs as in Fig. 208. median plate ; other been shown to exist in the Dipnoi. The two opercular bones aresmall, but retain on their inner surface small cartilages, whichappear to be remnants of branchial rays of the hyoid arch. Bran-chial rays, however, are not found on the gill-arches of modernDipnoi (Fig. 97). The Dipneumones differ from Ceratodus chiefly in the furthermodification of the dermal bones. The postorbitals and suborbitalsare gone. The ethmoid remains in front, and a large medianbone lying on the chondrocranium, and partly below the muscles,probably represents the occipital. The laterals project freelybehind over the muscles (Fig. 211). It is obvious that the cranialbones of the modern Dipnoi arc in a very specialised condition. TEETH 241 The nostrils in all Dipnoi are on the ventral surface of the are separate anterior or external nares leading into thenasal chambers, and posterior or inter
Size: 1588px × 1572px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
