. The elasmobranch fishes. Chondrichthyes. 58 THE ELASMOBRANCH FISHES 111 the olfactory region the capsules are seen in their relation to the elliptical nasal cartilages (, figs. 60. 63, and 64) surrounding the nasal aperture. Projections from the anterior and posterior margins of the ellipse meet and cross, usually forming of it a figure 8. A second anterior accessory process may be added as in Heterodontus {~, fig. 60), or may be more completely de- veloped as in Scyllium. In the rays the ellipse may be broken into segments. In Rhinohatis (fig. 64) the anterior and posterior projectio
. The elasmobranch fishes. Chondrichthyes. 58 THE ELASMOBRANCH FISHES 111 the olfactory region the capsules are seen in their relation to the elliptical nasal cartilages (, figs. 60. 63, and 64) surrounding the nasal aperture. Projections from the anterior and posterior margins of the ellipse meet and cross, usually forming of it a figure 8. A second anterior accessory process may be added as in Heterodontus {~, fig. 60), or may be more completely de- veloped as in Scyllium. In the rays the ellipse may be broken into segments. In Rhinohatis (fig. 64) the anterior and posterior projections forming the bridge are relativelj^ slender cartilages. In Myliohatis numerous accessor}^ projec- tions are Fig. 65. Dorsal view of cranium, Zygaena, left side. (Modified from Gegenbaur.) or., orbit; , postorbital process; , preorbital process. In a side view (figs. 66 and 68) the auditory, optic, and olfactory regions of the cranium are seen to advantage. With the exception of ChJamydosclachiis and the notidanids the auditory region is greatly modified superficially for the attachment of the hyoid arch. In most of the recent sharks the articulation is made by means of a deep pit (as is present in Heterodontus, fig. 66). In some of the rays a special part from the hyoid arch makes an extended articulation with this part of the cranium. Anterior to the auditory region is the enlarged orbit in which the eyeball rests. Its roof is usually formed by a supraorbital crest, modified posteriorly into a postorbital process {), and anteriorly into a preorbital process {). In the sharks the postorbital process is rarely extended. Exception must be made, however, of Zygaena, the hammerhead {, fig. 65) and its near ally, the bonnet shark, where it may be prolonged outward to meet the posterior part of the preorbital process. Exception should be made also of Chlamydosel- achus and the notidanids in which the postorbital process serves in suspend- ing the
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