. La biologie de l'amphibia. Les amphibiens. L'ORIGINE DE L'AMPHIBIA 9 de la centrum, bien que le basidorsal basiventral et généralement la sont représentés par des cartilages. Le pleurocentrum (interdorsal et interventral) peuvent rester sternèbre, formant la commune cartilagineux entre les vertèbres successives, ou la plus grande partie ne peut que l'ossifier "balle" de l'centrum. Si cette balle s'attache à la vertèbre en avant de lui, la vertèbre est procoelous ; si à l'un derrière, c'est opisthocoelous. . Phyllospondyli Embolomeri-contemporaine à la il y a eu lieu en Europe et un
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. The biology of the amphibia. Amphibians. THE ORIGIN OF THE AMPHIBIA 9 of the centrum, although the basidorsal and usually the basiventral are represented by cartilages. The pleurocentrum (interdorsal and interventral) may remain unossified, forming the cartilaginous joint between the successive vertebrae, or the greater part may ossify as the "ball" of the centrum. If this ball attaches itself to the vertebra anterior to it, the vertebra is procoelous; if to the one behind, it is opisthocoelous. Phyllospondyli.—Contemporaneous with the Embolomeri there occurred in both Europe and America a group of small Amphibia which were apparently destined to give rise to the frogs and salamanders at a later period. These were the Phyllos- pondyli (Fig. 4) as represented by Eugy- rinus in Lancashire, England, and Pelion in the Pennsylvanian of Linton, Ohio (Romer, 1930). Pelion retained such primitive features as an ectopterygoid, as well as an articulation of the pterygoid with the anterior margin of the basi- sphenoid region much as in the Embolo- meri. Large labyrinthodont teeth were present medial to the row of marginal teeth. Romer considers this form ances- tral to the typical branchiosaurs in which the labyrinthodont teeth were greatly reduced or lost and the pterygoid had a more posterior position and was presum- ably firmly fixed to the cranium. Typical branchiosaurs as represented in the late Pennsylvanian horizon of Bohemia had short, broad skulls, still retaining the tabulars and the dermosupraoccipitals, lost by all modern Amphibia (Fig. 5). The ribs were short and straight as in frogs and salamanders and were carried by transverse processes from the side of the vertebrae. Primitive frogsagree so closely with salamanders in vertebrae and skull that it would seem certain they had a common origin. The branchiosaurs resembled salamanders closely in body form. No fossils have been found with skull or pectoral girdle intermediate between that of branchiosau
