holes for arch bases 



A B 



Figure 6-23. Vertebra of Upper Devonian dipnoan, Jarvikia arcfica 

 as seen In end. A, and side view, B. (After Jarvik, 1952) 



the osteolepiform crossopterygian is most like the ichthyo- 

 stegid amphibian in terms of elements and interrelationships 

 of parts. It is possible that the rhachitomous type of the am- 

 phibian was derived from a rhachitomous fish. The problem 

 of the difference in ribs — the dorsal type in EulhenupUnm as 

 opposed to the ventral type in the dipnoan or coelacanth — 

 can be accounted for by modifying the view of Naef (Fig- 

 ure 6-73) that both ventral and dorsal ribs are involved in 

 the dorsal rib of the amphibian. The only remnant of the 

 ventral rib is the capitular head. 



Actinopierygian fishes 



Teleost The teleost, as represented by the salmon or perch, 

 generally has a holospondylous vertebra, that is, a one-piece 

 vertebra. The term is generally used in describing fish ver- 

 tebrae, but there is no special term for vertebrae having 

 separate parts. The most anterior trunk and the posterior 

 caudal vertebrae of the salmon or the first vertebra of the 

 perch have the neural arch sutured to the body (Figure 6-26). 

 The body is hour-glass shaped and amphicoelous. The 

 notochordal canal is constricted to a narrow passage at the 

 center of the body. The bone forming the body is spongy 

 except around the intervertebral swelling of the notochord. 



/ ligament 



sensory root foramen 

 ventral root foramen 



The neural arches of the anterior 20 to 25 vertebrae of the 

 salmon have double neural spines. Those of the perch fuse 

 at the tip. The neural arches of the posterior dorsals and 

 caudals of the salmon have the two halves fused. In the 

 salmon, the anterior neural arches (first 20 to 25 vertebrae) 

 are separate from the bodies, whereas, in the perch, only 

 that of the first vertebra is separate. In the salmon, these 

 free arches have their bases fitted into sockets. In the same 

 regions, there are calcified supradorsals between pairs of arch 

 components and lateral to the longitudinal ligament. The 

 supradorsals suggest the interneural connective from which 

 the pre- and postzygapophyses of the higher forms arise. The 

 neural arches of the perch have anterior and posterior basal 

 processes which overlap those of adjacent vertebrae to form 

 intervertebral articulations (Figure 6-26 D). 



In the salmon, the parapophyses of the anterior trunk 

 vertebrae are fitted into sockets of the body, and bear a 

 strong, ventral rib. Above the rib and attached by a liga- 

 ment is a small dorsal rib. In the perch, only the ventral 

 rib is developed. The parapophysis of a middle, trunk ver- 

 tebra of either the perch or the salmon has a strong lateral 

 process extending out anterior to the rib attachment. In a 

 posterior succession, these processes become longer and more 

 ventrally directed, and the rib articulation moves farther 

 out on them (Figure 6-40). In the anal region, these spines 

 are transformed, first, into the base of the hemal arch, and 

 then into the entire hemal arch including the hemal spine. 



The parapophyses of the most anterior vertebrae of the 

 perch are much reduced in size and are situated high up on 

 the side of the body. They are fused with the body and neural 

 arch. In the caudal region of the perch, the bases of the hemal 

 arches form a series of articulating processes (hemosphenes) 

 between the vertebrae. 



EMBRVOLOGICAL DEVELOPMENT In development, the noto- 

 chord of the teleost is at first large and unconstricted. The 

 myotomes lie very close to either side. There is little 



endocranium 



notochord sheath 



Figure 6-24. Vertebral structure of Lotimeria. A, anterior end of column; B, midthoracic region; C, 

 anterior caudal region; D, posterior port of column. (After Millot and Anthony, 1958) 



158 



THE VERTEBRATE BODY SKELETON 



