VERTEBRAL COLUMN 



353 



the development of anterior zygapophyses on the neural or haemal 

 arches which rest on corresponding processes in front, or these may 

 be supplemented by processes dorsal and ventral from the centra 

 themselves (Fig. 339). The basiventrals in the abdominal region 

 form outstanding processes of the centrum (parapophyses, * trans- 

 verse processes '), to which the pleural ribs may be articulated. 

 More dorsal ribs (epipleurals) generally are attached near the 



Longitudinal section through the vertebral column of A, Barbim vitlgari* ; and 13, 

 Naucnites ductur. (From Gegenbaur, VergL Anat.) c, notochord ; c.s, notochordal sheaths ; 

 ek, outer, and ik, inner bony layer ; jeb, intervertebral ligament ; >, space ; s, axial strand ; 

 v, centrum. 



parapophysis ; as they extend outwards in the horizontal septum 

 they are analogous, if not homologous, with the dorsal or true ribs 

 of Elasmobranchs, etc. Slender intermuscular bones (Fig. 305) 

 also frequently extend into the connective tissue septa from the 

 centra (epicentrals), or neural arches (epineurals). The tail in all 

 but the lowest families is completely homocercal (Figs. 63-65). As 

 a rule, the haemal arches of one or more of the most posterior 

 vertebrae become greatly expanded and are known as hypural bones 

 (Huxley [226], Kolliker [271], Ryder [378], Dollo [120]). The 

 liypurals may coalesce. In many groups, however, the tail tapers 

 to a symmetrical end, and acquires the appearance of a diphycercal 



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