160 Prof. E. D. Cope on the Systematic Relations of Fishes. 



the point of articulation and the distal segments in Polypterus 

 and the Sharks and Kays. In the former the distal segments 

 are articulated exclusively to the extremities of the proximal 

 pieces, which thus resemble, as well as represent, humerus and 

 femur, and render the limb pedunculated. The proximal pieces 

 are not continued distally, however, into the representatives of 

 the main axis, which, as demonstrated by the admirable stu- 

 dies of Gegenbaur, consist, after humerus, of radius, tarsals and 

 metatarsals, and thumb ; in the hind limb, of the line of the 

 tibia and inner toe. This continuation is observed in the Elas- 

 mobranchii, where, however, the divergent segments extend 

 along the sides of the proximal pieces to near, in some Rajida3 

 quite to the articulation with the scapular arch. In the true 

 fishes, including some of the old Ganoids already considered, 

 the divergent rays always reach this articulation, while the 

 number of proximal or basal pieces is diminished. These 

 pieces have been called by Gegenbaur the metapterygiura 

 (humerus), mesopterygium, and propterygium — the first being- 

 axial, the second and third being divergent from it. In Poly- 

 j)terus the propterygium and mesopterygium are largely deve- 

 loped ; in Sharks and Rays the propterygium is sometimes 

 small, sometimes wanting, while in the true fishes the propte- 

 rygium and mesopterygium are both wanting, excepting in 

 Amia^ Lejndosteus^ and the Sturgeons, where a cartilaginous 

 mesopterygium exists, according to Gegenbaur. This author 

 finds it rudimental in young Salmonidaj and Silurida?. Lastly, 

 in the true fishes the distal elements of the axis of the limb 

 are wanting, just as in Polyjiterus. 



In Dipnoi, on the other hand, we have this axis complete or 

 rather with greatly multiplied distal segments, and with or 

 without lateral radii. In the Australian Ceratodus Glinther 

 finds numerous lateral series on both sides of those of the axial 

 row. Hence the limb of this order is considered by Owen the 

 simplest or primary type ; and this proposition is abundantly 

 confirmed by the beautiful researches of Gegenbaur. The 

 foundation laid by this author for the history of the genesis of 

 limbs will ever be a landmark in the history of onodern theories 

 of creation (see his memoir, " Ueber das Skelet der Glied- 

 maassen der Wirbelthiere im Allgemeinen," &c., Jenaische 

 Med. Zeitschr. vol. v. p. 397). 



Important as are the characters that distinguish the several 

 groups indicated by the different types of structure of the limbs 

 and pelvis, they do not seem to me to warrant their recogni- 

 tion as classes equivalent to those of the six already pointed 

 out. Taking them together, there is a greater coherence also in 

 the structure of the brain and circulatory systems than would be 



