File:Chordate morphology (1962) (20611393355).jpg

Title: Chordate morphology
Identifier: chordatemorpholo00joll (find matches)
Year: 1962 (1960s)
Authors: Jollie, Malcolm
Subjects: Morphology (Animals); Chordata
Publisher: New York, Reinhold
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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CROSSOPTERYGIANS
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NEORHACHITOMES (TREMATOSAURS) BULLFROG LYRIOCEPHALUS COECILIANS Figure 6-18. The phylogeny of vertebral types os suggested by Williams (1939). notochord. The sclerotome, having a thickness of only one or a few cells, is very restricted. The close relation of muscle to notochord is explained by the fact that the larva is soon to swim actively. Because the sclerotome is so restricted, intrasegmental clefts cannot be detected. The first evidence of the skeleton is the appearance of the procartilaginous neural arches in the sheath of the neural canal. These arches extend up from the notochord on either side of the neural tube. Their bases lie in contact with a perichordal tube of cells. The peri- chordal tube is thickest in the intervertebral areas, where it forms an intervertebral ring of circularly arranged fusiform cells. This ring is thickest at the line of junction with the myo- septum (Figure 6-19). The myoseptum extends up and back along the neural arch and, in the caudal region, down and back along the hemal arch. As development progresses, the intervertebral ring be- comes cartilaginous and constricts the notochord (Figure 6-20). Ossification and chondrification appear at about the same time in the thin vertebral rings of the perichordal sheath. Externally the vertebral rings become bony, but the inner cartilage is continuous with the interverte- 154 THE VERTEBRATE BODY SKELETON

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