. Chordate morphology. Morphology (Animals); Chordata. B haemal spine Figure 6-16. Vertebral structure of an ichthyostegid. A, two dorsals as seen in lateral view; B, anterior view of dorsal; C, lateral view of caudal; D, anterior view of caudal. (After Jorvik, 1952) and postzygapophyses and long, posterolateral transverse processes. These processes are pierced at their base by an arterial canal in Necturus. In some amphibians the ribs are two-headed with what appears to be, but is not, a vertebral canal. There are no hypapophyses. There is one sacral with a thickened down-curving rib which su
. Chordate morphology. Morphology (Animals); Chordata. B haemal spine Figure 6-16. Vertebral structure of an ichthyostegid. A, two dorsals as seen in lateral view; B, anterior view of dorsal; C, lateral view of caudal; D, anterior view of caudal. (After Jorvik, 1952) and postzygapophyses and long, posterolateral transverse processes. These processes are pierced at their base by an arterial canal in Necturus. In some amphibians the ribs are two-headed with what appears to be, but is not, a vertebral canal. There are no hypapophyses. There is one sacral with a thickened down-curving rib which supports the ilium of the pelvic girdle, and there are 15 to 25 caudals. The second and succeeding caudals have hemal arches fused to the center of the vertebral body. The transverse processes of the first three caudals bear small ribs. Frog There are only 9 vertebrae and a urostyle in the col- umn of the frog. The first vertebra has bilateral articular facets for the occipital condyles of the skull, and a medial, odontoid process which extends forward between the con- dyles. There is a low neural arch with a slight spine and postzygapophyses. The second vertebra has broad trans- verse processes, as do the succeeding ones. The processes of the ninth vertebra, the sacral, attach to the ilia. These proc- esses represent both rib and diapophysis. Pre- and post- zygapophyses are well developed in the second though the eighth vertebrae, as are short, neural spines. There are no hypapophyses. With the exception of the first, next to the last, and last, the vertebrae are procoelous. The last verte- bra is convex anteriorly with a biconvex posterior surface; the next to the last is biconcave. The urostyle is a long splint which, posteriorly, is tubular for the remnant of the notochord. In its ossification, this column resembles the amniotes. The neural arches bear the transverse processes and unite with the body, which at first is tubular. The body appears as a crescent of bone above the
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