Early Development of Appendicular Skeleton of the Ostrich. 361 



more slender and they pass more backwards. The connecting band 

 of precartilage is relatively much smaller, and the pubis passes down 

 as a well-chondrified rod to a lower level than the ischium and 

 curves inwards towards its neighbour. There is still, however, no 

 symphysis, the two ends being considerably apart. 



The condition of the pelvis is particularly interesting as showing 

 that the avian type is not derived from one with the pubis and 

 ischium apart, as in the carnivorous dinosaurs, but rather a modifi- 

 cation of such a type as is seen in the pterosaurs. It further seems 

 to show that originally the pubis and ischium were directed down- 

 wards and that the backward direction is a late modification. 



Hind Limb. 



The hind limb of the adult ostrich is remarkable among birds for 

 having only two developed toes — third and fourth — and even the 

 fourth somewhat degenerate. There is, however, a rudiment of the 

 second metacarpal. In other respects the arrangement of parts is as 

 in normal birds. 



In the 10-day embryo the condition is remarkably interesting. 

 The tibia and fibula are fairly well chondrified and are of about 

 equal length. The tarsus is mainly precartilage, but the elements 

 are fairly distinct. The best defined is the elongated, partly chondri- 

 fied fibulare, which lies near the distal end of the fibula. Near the 

 distal end of the tibia is a large tibiale. When viewed from the 

 front it forms more than two-thirds of the proximal tarsal row. 

 When seen from behind, the tibiale is to a considerable extent hidden 

 by a large rounded intermedium. There seems to my mind little 

 doubt that this intermedium is quite a distinct element. In the 

 distal row of the tarsus is a group of three more or less fused 

 elements. These are evidently the second, third, and fourth tarsalia,. 

 and they are more or less distinct. To the radial side is a small 

 procartilaginous element, which is probably the first metatarsal, but 

 possibly the first tarsal. On the ulnar side lies a large procarti- 

 laginous rod, which is evidently the fifth metatarsal. The third and 

 fourth metatarsals are of large size, and partly chondrified. The 

 second metatarsal is much smaller and not distinctly chondrified. 

 Developing phalanges are seen on the second, third, and fourth 

 digits. 



In the 11-day embryo all the elements are very much better 

 developed, and the changes in some respects are remarkable. The 

 lower end of the tibia is relatively very much larger, and in corre- 

 spondence with it the anterior side of the tibiale is equally broad and 



