Ratite or Struthious Birds 19 



Another very wonderful bird is the Hoatzin {Opisthocomus 

 hoaziri) of South America. It seems to be a survival 

 on the earth of some ancient form, for it possesses features 

 quite different from those of the birds of the present day, 

 and it is also probably the surviving representative of a 

 type once widely distributed over the earth, as Professor 

 Milne-Edwards informs me that the bones of his genus 

 Filholornis, from the phosphate deposits of Chaux in the 

 south of France, can only be compared with those of 

 Opisthocomus, and hence it would seem that Hoatzins of 

 some kind or another formerly lived in Europe. 



In appearance the Hoatzin is like a Game-bird, and it 

 was for many years considered to belong to the family of 

 Curassows (Cracidce), which inhabit the South American 

 continent. Its anatomy, however, has recently been more 

 closely studied, and shows that it possesses characters quite 

 different from those of the Galliformes, and hence the genus 

 Opisthocomus is now generally allowed to constitute a 

 distinct Family, if not indeed a distinct Order, of Birds. In 

 the Ratite Birds we have seen that one of the most striking 

 features in their skeleton was the complete absence of any 

 keel to the sternum or breast-bone, and in Opisthocomus we 

 find another development of this keel, differing from that 

 of other birds. The keel is in fact only found on the 

 posterior part of the sternum, and falls away gradually 

 on the anterior portion of the latter, while the other 

 bones belonging to this part of the skeleton, the coracoids 

 and the '■ merry-thought " or furcula, are fused together in a 

 manner unlike that of any other known bird. The reason 

 for this peculiar arrangement is now recognized as a pro- 

 vision for the enormous crop with which the Hoatzin is 

 provided. 



The single species of the genus OpistJiocomus is an 

 inhabitant of the rivers of Amazonia and the northern 

 portion of South America from Guiana to Ecuador and 



