. Elements of Comparative Anatomy. APPENDICULAR SKELETON" OF VERTEBEATA. 479. Fig. 264. Primary skeleton of the thoracic fin of Aci- penser ruthenus, after the removal of a portion of the secondary skeleton. B Basale of the meta- pterygium. R Bony marginal ray of the secondary skeleton of the fin, only figured in part. secondary skeleton of the fin-rays (h). Basal pieces can be seen in a few only, and it is difficult to refer these even to their primitive significance. The arrangements which obtain in the Granoidei "would lead us to regard the basale of the metapterygium^ and the bas
. Elements of Comparative Anatomy. APPENDICULAR SKELETON" OF VERTEBEATA. 479. Fig. 264. Primary skeleton of the thoracic fin of Aci- penser ruthenus, after the removal of a portion of the secondary skeleton. B Basale of the meta- pterygium. R Bony marginal ray of the secondary skeleton of the fin, only figured in part. secondary skeleton of the fin-rays (h). Basal pieces can be seen in a few only, and it is difficult to refer these even to their primitive significance. The arrangements which obtain in the Granoidei "would lead us to regard the basale of the metapterygium^ and the basalia of some of the rays, as being the most constant constituents of these pieces. In consequence of their having the same function they have the same form, so that it is impossible to show that they have any connection with the primary stage, except by referring them back to the skeleton of the Ganoid fin. In many divisions of the Teleostei these pieces undergo great changes, in addition to being diminished in number. They are, for instance, intimately attached to the shoulder- girdle, and immovably connected with the parts of which it is made up (Cataphracti). In this way we are able to make out a con- tinuous series from the well-developed skeleton of the fin in the Selachii to that which is found in the Teleostei; the most important changes consist in the gradual reduction of smaller or larger parts. Reduction first affects the periphery, and then the base, so that the latter is the most constant portion. The decrease in size which the primary skeleton suffers is made up for by the appearance of ossifications of the integument, which consist, as in the unpaired fins, of jointed or firm bony rays, and are developed on both surfaces of the fin. Gegenbaue, C, Untersuchimgon zur vergleich. Anatomic der WLrbelthiere. II. Leipzig, 1865. § 363. In the skeleton of the fore-limb of the higher Vertebrata we are able to recognise the stem of the archipterygium, with rays attached to
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