A treatise on zoology . ront by cartilage {Gadus, p. 276), sometimes expanding behindinto large plates spreading towards the middle line (Siluroids, etc.,Fig. 305). The vertebral centra show no signs of compound structure. Asa rule, they are more or less solid and biconcave (Figs. 336, 337),the notochord in living genera being usually constricted to a merefibrous thread (Goettc [167], Grassi [182], Scheel [385]). Thecentra are generally, but not always, co-ossified with the arches andthese with the spines. Intervertebral articulations are formed by VERTEBRAL COLUMN 353 the development of anter
A treatise on zoology . ront by cartilage {Gadus, p. 276), sometimes expanding behindinto large plates spreading towards the middle line (Siluroids, etc.,Fig. 305). The vertebral centra show no signs of compound structure. Asa rule, they are more or less solid and biconcave (Figs. 336, 337),the notochord in living genera being usually constricted to a merefibrous thread (Goettc [167], Grassi [182], Scheel [385]). Thecentra are generally, but not always, co-ossified with the arches andthese with the spines. Intervertebral articulations are formed by VERTEBRAL COLUMN 353 the development of anterior zygapophyses on the neural or haemalarches which rest on corresponding processes in front, or these maybe supplemented by processes dorsal and ventral from the centrathemselves (Fig. 339). The basiventrals in the abdominal regionform outstanding processes of the centrum (parapophyses, trans-verse processes ), to wdiich the pleural ribs may be dorsal ribs (epipleurals) generally are attached near the. Longitudinal section llirough tlie \-ertebral column of A, Barhtis vulgaris; and IJ,Naucrates diictor. (Prom Gegeiibaiir, Vergl. AiuU.) c, notochoid ; , iiotochordal sheaths ;eJc, outer, and ik, inner bony layer ; jrb, intervertebral ligament ; r, space ; s, axial strand :V, centrum. parapophysis ; as they extend outwards in the horizontal septumthey are analogous, if not homologous, with the dorsal or true ribsof Elasmobranchs, etc. Slender intermuscular bones (Fig. 30o)also frequently extend into the connective tissue septa from thecentra (epicentrals), or neural arches (epineurals). The tail in allbut the lowest families is completely homocercal (Figs. 63-65). Asa rule, the haemal arches of one or more of the most posteriorvertebrae become greatly expanded and are known as hypurjil bones(Huxley [226], KoUiker [271], Eyder [378], Dollo [120]). Thehypurals may coalesce. In many groups, however, the tail tapersto a symmetrical end, and acquires the appearanc
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