36o PRIMARY FACTORS OF ORGANIC EVOLUTION. 



crease in the proximal connections, exactly similar to 

 that which took place in the horse-line, in a different 

 order of Mammalia. 



In review I now cite as examples of homoplassy: 



First, as regards the development of the tongue- 

 and-groove ankle-joint. This has been developed in- 

 dependently along four distinct phyla, viz., in the lepo- 

 rid Glires, the Carnivora, and the even and odd toed 

 Diplarthra. 



Second, the wrist-joint. The faceting of the radial 

 surface has appeared independently in the perissodac- 

 tyle and artiodactyle lines, but is best developed in the 

 latter. Also it appeared independently in the separate 

 suoid and booid lines in the latter suborder. 



Third, the trochlear crest of the elbow-joint ap- 

 peared independently in the perissodactyle and artio- 

 dactyle Diplarthra, and in the leporid Glires (the rab- 

 bit family). 



Fourth, the round head of the radius appeared in- 

 dependently in the lines of the Edentata (ant-eater) 

 and Quadrumana, under the stress of supination of 

 the hand. 



Fifth, the development of cusps with crescentic sec- 

 tion out of cusps with round section has occurred in 

 the widely different groups of the multituberculate 

 Prototheria, and the selenodont Artiodactyla. In the 

 former the crescents are transverse, since the thrust of 

 the teeth in use is longitudinal : in the latter they are 

 longitudinal, since the thrust of the jaws is transverse. 



Sixth, the deep plication and hypsodcnty of molars 

 appeared independently in the Glires, Tillodonta, Pro- 

 boscidia, Sirenia, Perissodactyla, and Artiodactyla ; 

 and probably in the Edentata and Toxodontia. 



Seventh, increase in the length of the legs has en- 



