. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 32 Biology of the Vertebrates The name holocephali (holos, whole; cephalon, head) is given to them because the upper jaw is immovably fused with the cranium after the man- ner of higher forms, instead of being indirectly suspended by means of ligaments and cartilages as in elasmobranchs. Of the three living genera, Chimaera (Fig. 21) is found on the Pacific coast of North America, as well as on the coasts of Europe and Japan and at the Cape of Good
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 32 Biology of the Vertebrates The name holocephali (holos, whole; cephalon, head) is given to them because the upper jaw is immovably fused with the cranium after the man- ner of higher forms, instead of being indirectly suspended by means of ligaments and cartilages as in elasmobranchs. Of the three living genera, Chimaera (Fig. 21) is found on the Pacific coast of North America, as well as on the coasts of Europe and Japan and at the Cape of Good Fig. 21. Chimaera, a holocephalian fish. (From Newman, The Phylum Chordata, copyright 1939, by permission of The Macmillan Company, publishers. After Bridge.) b. Subclass OSTEICHTHYES The modern bony fishes are grouped into the subclass Osteichthyes. At least a part of the skeleton is ossified. Over the skull and pectoral girdle region, investing bony plates are laid down in the dermal portion of the skin. The gills are protected by an opercular fold which has investing bony supports. No claspers are present. Air bladders, outgrowths from the pharynx, are present in all bony fish except a few teleosts. There are three orders of bony fishes: (1) crossopterygii; (2) dipnoi; and (3) actinopterygii. (1) crossopterygians.—The Crossopterygii are commonly called lobe-finned fishes because each of their paired fins has a thick, fleshy basal lobe. The skeletal support of this fin consists of a single basal element fol- lowed by two bones beyond which are a number of irregular small bones. This condition suggests the plan of the land type of appendage. Other fea- tures of this group are: (1) air bladders serving as lungs; (2) a spiral valve in the intestine; and (3) nasal cavities opening into the roof of the mouth cavity. These fish are believed to be the ancestors of land animals. All members of this group are extinct with the exception of Latimeria which is represented by one specim
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