. Bulletin of the British Museum (Natural History). OSTEOLOGY OF THE D E NT I CI PI TI D A E 241 Both the epi- and ceratohyals of each side are traversed by a tubular canal housing the hyal artery. The tube opens anteriorly on the dorsal aspect of the ceratohyal and posteriorly it opens on the lateral face of the epihyal. The paired dorsal hypohyals (Text-figs. 22 and 23) are small, ovoid bodies closely applied to the posterior tip of the basihyal on its ventral surface. The ventroanterior tips of the dorsal hypohyals articulate with the underlying postero- dorsal tips of the ventral hypohyals
. Bulletin of the British Museum (Natural History). OSTEOLOGY OF THE D E NT I CI PI TI D A E 241 Both the epi- and ceratohyals of each side are traversed by a tubular canal housing the hyal artery. The tube opens anteriorly on the dorsal aspect of the ceratohyal and posteriorly it opens on the lateral face of the epihyal. The paired dorsal hypohyals (Text-figs. 22 and 23) are small, ovoid bodies closely applied to the posterior tip of the basihyal on its ventral surface. The ventroanterior tips of the dorsal hypohyals articulate with the underlying postero- dorsal tips of the ventral hypohyals through a very small point of contact. Posteriorly they approach closely the anterior tip of the first basibranchial but do not actually contact that bone. The ventral hypohyals (Text-figs. 22 and 23) are much larger, pyramidal bones, also separated narrowly in the midline. They articulate with the dorsal hypohyals and more extensively, with the head of the ceratohyals. The unpaired, median basihyal is a poorly ossified elongate bone (Text-fig. 22), hemicyhndrical in section and somewhat broader anteriorly than posteriorly. It articulates with the dorsal hypohyals, and with the anterior tip of the first basi- branchial. Continuous with its cartilaginous anterior tip is a small hemispherical nubbin of cartilage (Dr. G. Nelson, who has examined the material, interprets this as a case of secondary segmentation of the basihyal, in his experience an unusual occurrence). No teeth are present on any part of the hyal skeleton. The urohyal is a poorly ossified, elongate and rather slender bone; except for a short distance anteriorly it has a double ventral margin, the bone being an inverted " V "in cross-section. The branchiostegal rays (Text-figs. 19 and 20) have been mentioned briefly above. In all specimens examined by Dr. Clausen and me there are five pairs of rays. Of these, four articulate with the ceratohyal, and one with the epihyal. The branchiostegals show an antero
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