DEVELOPMENT OF PBLVIO GIKDLE IN THE OHIOK. 25 



separated, and the two proximal elements fuse together. Next, 

 the proximal part begins to fuse with the tibia, which has 

 grown more than the fibula, so that the latter no longer reaches 

 the tarsus. The posterior lower edge of the tibia first becomes 

 continuous with the proximal tarsal cartilage, while the ante- 

 rior face of the latter gives off an upward process, the so-called 

 "ascending process of the astragalus," which fits into a 

 groove in the tibia, and remains for a long time separate from 

 it. At about the same time the distal part of the tarsus fuses 

 with the metatarsals, first with the second, next with the 

 fourth, and lastly with the third. All these processes take 

 place while the tarsus is still cartilaginous. 



Morse ^ describes, in the tarsus of the embryo bird, an inter- 

 medium, which at first projects upwards between the distal 

 ends of the tibia and fibula. Later, the tibiale and fibulare 

 fuse behind it, while the tibia extends so as to cover the 

 whole proximal surface of the tarsus, and the intermedium 

 remains fitting into a groove on the anterior face of the tibia. 

 It has a separate centre of ossification, but becomes anchylosed 

 with the tibiale and fibulare, forming what is called the 

 ascending process of the astragalus. 



Both Baur and myself fail to find a separate origin for the 

 intermedium. Baur describes the ascending process as an out- 

 growth from the tibiale, in which view I am inclined to concur. 

 • But the deviation of our views from that of Morse may, per- 

 haps, be explained by the fact that while Baur worked only at 

 the chick, duck, sparrow, jiigeon, and blackbird, and I only at 

 the chick, Morse investigated some aquatic birds — the tern, 

 penguin, petrel, gull, &c. 



In conclusion, I have to thank Dr. Gadow for his kindness 

 in giving me help and advice during the course of my work. 



E. S. Morse, " On the Identity of the Ascending Process of the Astragalus 

 in Birds with the Intermedium," ' Anniversary Memoirs of Boston Society of 

 Natural History,' 1880. 



