'300 VERTEBRATE ZOOLOGY 



The jungle-fowls deserve special mention because it is from 

 them that our domestic poultry have been derived. Four distinct 

 species of jungle-fowl are known, all of them native to the dense 

 jungles of the Indo-Malayan region. Of these it is believed that the 

 red jungle-fowl (Gallus gallus) has given rise to all of the domestic 

 breeds of poultry. The breed known as the black-breasted game has 

 retained more completely than any of the others the characters of the 

 wild ancestor. The most extreme deviations from the primitive 

 characters of the species are seen in the Japanese tosa fowl, in which 

 the tail feathers have been known to reach a length of fifteen feet, 

 and the cochins, with their short, plump appearance and feathered 

 shanks. 



The hoactzin, representing the fourth sub-order (Opisthocomi) , 

 is one of the most curious of birds. In the adult condition it is not 

 unlike a small type of pheasant, but it has certain anatomical char- 

 acters that set it apart from all other birds: the breast bone is wider 

 behind than in front; the keel of the sternum is confined to the poste- 

 rior part; the crop is extremely large and muscular, invading the space 

 usually taken up with pectoral muscles and the anterior part of the 

 sternum; and the bones of the shoulder girdle are fused completely 

 to one another and to the sternum. The most remarkable features of 

 the hoactzin, however, concern the young bird, which, when newly 

 hatched, has a well-developed clawed thumb and index finger on the 

 wing, reminding one of the condition in Archceopteryx. By means of 

 these wing-digits and the feet which are extraordinarily large and 

 strong for a young bird, these youngsters are able to clamber about 

 among the branches and hunt for their own food. They are really 

 practically quadrupedal in the use of both pairs of limbs in climbing. 

 It is believed by some writers that the juvenile characters of the hoact- 

 zin are reminiscences of an Archseopteryx-like ancestry. Inasmuch, 

 however, as they belong to one of the more highly specialized groups 

 of birds, and inasmuch as no other known type of bird exhibits 

 similar juvenile characters, it seems more likely that these characters 

 are adaptive, juvenile specializations. In view of all of the peculiari- 

 ties of the hoactzins it is difficult satisfactorily to classify them in 

 any order; but the rather strong resemblance of the adult to the 

 pheasants seems to place them among the Galliformes. 



