. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 584 Biology of the Vertebrates Lizards and possibly some other reptiles have what appears to be only the superior temporal fossa, the parapsid condition, although there is still considerable doubt concerning the relationships of the parts of the skull in these animals. Turtles (Fig. 499) are anapsid but they are believed to have acquired this condition secondarily as a result of the filling in of the fossae by enlarge- ment of the individual bones. 7. Vert
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 584 Biology of the Vertebrates Lizards and possibly some other reptiles have what appears to be only the superior temporal fossa, the parapsid condition, although there is still considerable doubt concerning the relationships of the parts of the skull in these animals. Turtles (Fig. 499) are anapsid but they are believed to have acquired this condition secondarily as a result of the filling in of the fossae by enlarge- ment of the individual bones. 7. Vertebrate Skulls (a) Cyclostomes.—The skull of cyclostomes (Fig. 502) is quite aber- rant from that of other vertebrates. In the embryonic "ammocoetes stage" of Petromyzon, the parachordalia and trabeculae of the brain-case floor are evident and normal, as well as the otic capsules that surround the ears, but a cartilaginous envelope does not entirely surround the brain, since the roof of the brain case is completed in fibrous connective tissue, while the absence of. Fig. 502. Lateral view of skull of Petromyzon. 1, horny teeth; 2, annular cartilage; 3, anterior labial cartilage; 4, posterior labial cartilage; 5, nasal capsule; 6, auditory capsule; 7, dorsal portion of trabeculae; 8, lateral distal labial cartilage; 9, lingual cartilage; 10, branchial basket; 11, carti- laginous cup supporting pericardium; 12, sheath of notochord; 13, anterior neural arches, fused together. (From Shipley and MacBride, after Parker.) jaws entirely changes the character of the anterior part of the skull. The skeletal structures of the large tongue may possibly be homologous with the lower jaws of fishes. At any rate the tongue bears rasping epidermal teeth and is bilateral in origin like the lower jaws. The cartilaginous elements which lie anterior to the tongue and support the jawless mouth seem to be peculiar to cyclostomes. They are obviously necessary adaptations on account of the su
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