8. Abstammungslehre. 321 



in heavy animals, they tend to disappear, e. g. the Giraffe and genus Bos. 

 Numerous cases are quoted in support of these views. 



Doncaster (Cambridge). 



888) Gregory, W. K., The Lim bs ofEryops and the Origin ofPaired 

 Limbs from Fins. 



(New York Academy of Science, Section of Biology. 13. Februar 1911.) 



In a skeleton of the termospondylous Amphibian Eryops megacephalus 

 Cope, from the Permion of Texas, which is now being mounted in the Ame- 

 rican Museum, the limbs are of special interest. Many resemblances to the 

 contemporary reptile Diadectes are seen in the stout, long coraco-scapula, 

 the short, wide headed humerus, with its very wide, prominent and backwardly 

 directed entocondyle, in the short fore-arm, in the very heavy, solid pelvis, 

 stout femur and fully ossified carpus and tarsus. In the Charakter of its 

 limbs Eryops was on the whole nearer to Sphenodon than to the Urodeles, 

 though far more archaic than the former. As shown by the facets, the nu- 

 merus and femur were held almost at right angles to the body, the opposite 

 feet being held very widely apart. 



The generalized character of the limbs of Eryops with respect to those 

 of higher Tetrapoda invite renewed inquiry into the origin of paired limbs 

 i'rom fins. The limbs of known Branchiosaurs and Microsaurs do not carry 

 us very far back toward any known type of fish fin. In these Orders the 

 cylindrical shafts of the long bones, with cartilaginous ends, the cartilaginous 

 carpus and tarsus, the weak Shoulder girdle and pelvis suggest a secondary 

 adaptation to aquatic habits. 



From the work of Thacher, Goodrich, Dean, B. C. Osburn and others, 

 it seemed probable that the paired fins of fishes, like the median fins, have 

 evolved from wide-based fins with serially arranged basal and radial carti- 

 lages. After the formation of the primary Shoulder girdle and pelvis and of 

 the pro-, meso- and metapterygia by fusion and growth the basals, the various 

 types of paired fins seen in Plagiostomes, Chimaeroids, Pleuracanths, Dipnoans, 

 Crossopterygians and Actinopterygians seem to have arisen in each case through 

 the Protrusion of the basal cartilages, differential growth and shifting of the 

 radiale, and in some cases (e. g. Pleuracanths, Crossopterygians, Dipnoans) 

 also through the extension of the radiale around to the post-axial side of the 

 metapterygial axis. If the Amphibia have descended from the common stem 

 of the Dipnoi and Crossopterygii (as seemed likely) then it was entirely pro- 

 bable that their paired fins had been transformed into limbs through the 

 further Protrusion of the proximal cartilages, differential growth and regrou- 

 ping of the more distal cartilages, reduction of the dermal rays. This struc- 

 tural change may well have been in large part effected before the air-breathing 

 proto-ampbibians had left the water, owing to the assumption of a new func- 

 tion in the paired fins, i. e. pushing against solid objects such as roots, in 

 the stagnant water, instead of merely steering. A study of the pectoral girdle 

 and fins of Sauripteris, a Bhizodont Crossopterygian of the Uper Devonian, 

 in comparison with those of Polypterus and with the limbs of primitive 

 Amphibian, had suggested the following provisional homologies: 



Crossopterygian Tetrapod 



„Infra clavicle" = Clavicle 



„Clavicle" (of Parker) =• Scapula 



„Supra clavicle" = Cleithrum 



„Coracoid" (Hypocoracoid) = Coracoid (or precoracoid?) 



