. The elasmobranch fishes. Chondrichthyes. 122 THE ELASMOBRANCH FISHES. Fig. 121. Teeth of Heptanchus indicus. donald and Barron.) (From Mac- mouth and nasal pits in He/ptanchus are not connected by oronasal grooves characteristic of some of the Elasmobranchs. The buccal cavity proper is large and spacious. Its floor is lifted up by the basihyal cartilage, forming a skeleton for the so-called tongue. The mucous membrane lining the mouth is provided both dorsally and ventrally with numerous stomodeal denticles (see p. 24, fig. 27c) which, as we have seen in a study of the integument, are modi-
. The elasmobranch fishes. Chondrichthyes. 122 THE ELASMOBRANCH FISHES. Fig. 121. Teeth of Heptanchus indicus. donald and Barron.) (From Mac- mouth and nasal pits in He/ptanchus are not connected by oronasal grooves characteristic of some of the Elasmobranchs. The buccal cavity proper is large and spacious. Its floor is lifted up by the basihyal cartilage, forming a skeleton for the so-called tongue. The mucous membrane lining the mouth is provided both dorsally and ventrally with numerous stomodeal denticles (see p. 24, fig. 27c) which, as we have seen in a study of the integument, are modi- fications of placoid scales. In the region just within the crescent of teeth the lining of the mouth is thrown into heavy folds, which lie over the concen- tric rows of tooth buds. The teeth of Heptanchus (see fig. 48, facing p. 44) consist of a heavier lower series and a cuspidate upper series. The first tooth in the lower row of Hep- tanchus maculatus, like that for H. indicus (fig. 121), is unpaired and without a me- dian cusp. On either side of it are seven teeth, the most posterior of which is cusp- less and is followed by sev- eral rows of smaller flat nodules not shown in figure 48. The first of the large teeth is provided with a se- ries of three conules on the median margin and usually six larger conules on the lateral margin. Other lower teeth including the sixth, though differing in size, are essentiallj^ like the first paired tooth. Unlike Heptanchus indicus (fig. 121) there is usually no unpaired upper tooth in Heptanchus maculatus. The first paired tooth above bears a long fang which is directed downward; at its sides are small basal denticles like those in Heptanchus indicus. The second tooth and the ones following, although larger, differ from the first only in that they possess median conules and outer cusps, several of which are present on each tooth. Pharynx and Associated Structures The pharyngeal part of the tract is wide from side to side and depressed or
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