On the Tarsus and Carpus of Birds. 



151 



some mammalia these two latter bones are connate, e. g., in 

 the carnivora ; while in others they are free. 



The position of this pretibial bone appears anomalons, but 

 when we consider the remarkable displacement of other 

 bones in the bird's leg, the occurrence of this new tarsal in 

 such a place, is by no means unreasonable. The displace- 

 ment of certain bones in the bird's leg, is the result, as it 

 were, of lateral compression, or rather lateral contraction. 

 The fibula is always reduced to a mere splint bone, and is 

 closely appresscd to the tibia. The metatarsals are so 

 crowded together that the proximal end of the mid-meta- 

 tarsal is forced back, so that the flanking metatarsals actually 

 meet in front. All these ultimately anchylose and form a 

 single bone. The first metatarsal is reduced to a half, or a 

 third the size of the others, and is often crowded behind the 

 others. The two proximal tarsal bones at first, stand one 

 at the end of the tibia, and the other at the end of the fibula, 

 the tibiale being actuall}^ as wide as the distal end of the 

 tibia (see plate iv, fig. 1) ; yet in a short time these two 

 tarsal bones are gradually 

 brouo'ht too;cther, and as the 

 fibula becomes reduced in 

 comparative size, the tibia 

 takes on an accelerated 

 growth, so that its distal end 

 equals in width the two tar- 

 sals to which it finally unites. 



To show still more plainly 

 the reasons for believing that 



Fig. G 



Fig. 7. 



The intermedium in the three figures is 

 represented black. 



Fig. 0. Representing- lower portion of 

 leg of Sulamandra maculosa, copied from 

 Gegenbaur, with distal tarsals omitted. 



Fig. 7. Spizella sociaiis copied from flg. 

 1, plate iv, of tliis paper, with intermedium 



the pretibial bone or At y man iutroduced. 



^ "^ Fig. 8. Ideal figure showing true position 



represents the intermedium, ot intermedium inrelation to proximal tar- 

 ^ ' sal bones. 



the following diagrams are f. Fiimia. T' ^v '•"; 



C! o /. fibulare. t. ttbuue. 



presented. The intermedium "• <^««^™^«- 

 is represented black. Figure 6 represents the intermedium 

 and its associate tarsals in relation to the tibia and fibula of 

 Salamandra maculosa, after Gegenbaur. 



