. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 234 CLASSIFICATION OF Fig. 236. Diagrams of cyclospondylous (^) and asterospondylous (^) vertebras. Calcifications of cartilage black. line between calcified cartilage and bone. Membrane bones are absent in all recent forms, but in some fossils the dermal scales united to form an ex- tensive armor. In some the vertebral centra are entirely of cartilage. When lime is deposited in them it may take two shapes, either laid down in concentric areas (cyclospondy- lous type), or in a ra- dial manner (astero- spondylou
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 234 CLASSIFICATION OF Fig. 236. Diagrams of cyclospondylous (^) and asterospondylous (^) vertebras. Calcifications of cartilage black. line between calcified cartilage and bone. Membrane bones are absent in all recent forms, but in some fossils the dermal scales united to form an ex- tensive armor. In some the vertebral centra are entirely of cartilage. When lime is deposited in them it may take two shapes, either laid down in concentric areas (cyclospondy- lous type), or in a ra- dial manner (astero- spondylous). In the diplospondyli and in the tail of some skates an embolomerous condition occurs. In all recent forms the neu- ral arch is converted into a closed canal by the insertion of intercalary pieces betweeen the neural processes and spine. The cranium is a solid box without sutures. In its roof there may be one or two gaps (f ontanelles) closed by membrane. The pterygoquadrate is never firmly united to the cranium, but either articulates directly with it (amphistylic, Fig. 237), or is supported by ligaments and by the interven- tion of the hyomandib- ular between the hinder end of the pterygoquad- rate and the otic region of the cranium (hyo- stylic. Fig. 162), thus forming a suspensor for the jaws. The pterygoquadrate forms the upper jaw, but is re- enforced in many spe- cies by labial cartilages. In some extinct elasmobranchs girdles are apparently absent, but in all recent forms they are well developed. The pectoral girdle consists of a simple U-shaped. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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