TABLE 6-1 TERMS, ADJECTIVES, USED TO DESCRIBE THE VARI- 

 OUS KINDS OF VERTEBRAL STRUCTURE IN TETRA- 

 PODS 



Temnospondylous temno or latnno, to cut; spondylos, vertebra 



Vertebra consisting of several parts; formerly designated as 

 having the arch separated from the body as opposed to stereo- 

 spondylous. Several of the following more specific terms are 

 now used in place of temnospondylous. 



Rhachitomous rhachts or rkachites, spine, of the spine; tomos, cut or 

 section 



Referring to the "cut up" spine, or having two pairs of arch 

 components. The body is in two parts; a larger anterior inter- 

 centrum and a smaller posterior centrum. The latter is the 

 second "arch" component. 



Emboiomerous fmbului, object thrust in; meros, a part 



Referring to the separate and equally, or nearly equally, 

 developed intercentrum and centrum. Literally another part 

 thrust in. 



Stereospondylous slereus, solid; spondylos, vertebra 



Referring to a vertebra with a single body composed entirely 

 or essentially of the intercentrum. The neural arch may be 

 detached (Figure 6-18, Maslodomaurus). 



Lepospondylous /epis or lepos, a scale; spondylos, vertebra 



Referring to shell-like or husk-vertebrae — a type of vertebra 

 that does not extend beyond an amphicoelous stage and has 

 a notochordal perforation through the body. This type in- 

 cludes the primitive or neotenic frogs, and salamanders. The 

 vertebra may be holospondylous, all in one piece, or the neu- 

 ral arch may be detached as in the adelospondylous type (see 

 below). 



Phyllospondylous /iA^/Zon, leaf or leaf-like; spondyloi, vertebra 



Referring to the shell-like (perichondrally ossified) discon- 

 nected pieces of an otherwise rhachitomous type. An example 

 is Amphibamus (Figure 6-15). 



Adelospondylous adelos, concealed, not known; spondylos. vertebra 



Vertebrae with a detached neural arch as in Lysoriiphiis; other- 

 wise, a lepospondylous type. 



Neorhachitomous neos, new or recent 



A rhachitomous type approaching the stereospondylous by re- 

 duction in size of the centrum component. The term applies 

 to a late group of amphibians of rhachitomous ancestry. 



Holospondylous holos, whole or entire; spondylos, vertebra 



Each vertebra consists of a single piece whether it is solid or 

 husk. 



bral cartilages. As development proceeds, the middle of the 

 vertebra becomes quite constricted and cartilage may in- 

 vade the notochord (Figure 6-19 A); the ends of the 

 vertebral body flare out around the intervertebral cartilage. 

 In the caudal region of the salamander, the hemal arches 

 appear below the neural arches and become attached to the 

 body. A circlet of connective tissue grows into the interver- 



tebral cartilage to form the joint. A ball-like intervertebral 

 body may be separated by this connective tissue, thus form- 

 ing an amphicoelous joint; the greater part of the interver- 

 tebral cartilage can remain attached to the more posterior 

 vertebral body to form an opisthocoelous articulation or to 

 the anterior vertebral body to form a procoelous joint. 

 In some species the intervertebral body appears to be split 

 equally between the vertebrae. 



A separate supradorsal cartilage forms in the neural arch 

 above the neural canal. This gives rise to the pre- and post- 

 zygopophyses as well as to the short spine. The ribs appear 

 as separate chondrifications as do the "rib bearers." The 

 origin of the rib bearer in the various salamanders suggests 

 that it is a compound structure of both dorsal and ventral 

 rib heads. The definitive rib, whether two-headed or not, is 

 not entirely comparable to the reptilian rib, which is bas- 

 ically a dorsal one with its capitular head derived from the 

 ventral rib. The ribs of Urodela and Anura are thought to 

 be dorsal ones, the ribs of the Apoda ventral ones. 

 General observafions The vertebral body of the amphibian 

 forins between intervertebral rings very much as it does in 

 the previous groups (Figure 6-21). Whereas the reptile or 

 mammal vertebral body lies generally behind the rib, that 

 of the amphibian projects well in front. This suggests that 

 the intercentrum was incorporated into the body or, per- 

 haps, that the body is of intercentral rather than central 

 origin. The craniovertebral articulation of the amphibian 

 is quite distinctive. 



Choanate fishes 



Dipnoan In recent dipnoans, vertebral bodies are not 

 developed, although cartilaginous blocks occur in the tail 

 region (Figure 6-22). "Centra" have been observed in the 

 Devonian fossil forms, Diplerus and Rhynchodiplerus, but the 

 details of these are not known. Jarvik (1952) has described 

 the vertebral bodies of two kinds of dipnoans froin the 

 uppermost Devonian of Greenland. One of these, Soeder- 

 berghia or form A, is like Rhytuhodipterus, the olher, J annkia 

 or form B, resembles the fossil genus Fleurantia in external 

 shape. In these forms, no arcualia (neural or hemal arches) 

 have been seen; however, long ribs occur in form A. 



The vertebral bodies of form B (Figure 6-23) have been 

 sectioned (by grinding), but their detailed histological struc- 

 ture was not revealed. There is evidence of concentric layer- 

 ing of trabecular material around the central axis (noto- 

 chord axis). The tissue may have been bone, but more 

 probably, was calcified cartilage. 



The vertebral bodies are amphicoelous, those of A being 

 pierced by a narrow notochordal canal. In B, the canal is 

 lacking, and there are paired dorsolateral and ventrolateral 

 openings, which probably were occupied by the cartilagi- 

 nous arcualia (or arches). The form of the body in B sug- 

 gests invasion of the notochordal sheath by sclerotome cells. 

 This is supported by observations of the development of the 



THE VERTEBRAL COLUMN 



155 



