554 STEREORNITHES. 



is necessary to mention here an assemblage of giant flightless birds, which were 

 abundant during the Miocene Tertiary in Patagonia and parts of Argentina. 

 These Stereomithes, as they are called, certainly cannot be included among the 

 modem flightless group of giant birds, and it is uncei'tain whether they can claim 

 a place with the preceding orders in the great subclass of Carinatcn ; so that they 

 must, accordingly, be allowed to constitute a group by themselves, of which the 

 exact serial position cannot yet be fixed. Attaining gigantic dimensions (the tibia 

 of one species being upwards of 30 inches in length), these Patagonian birds are 

 especially characterised by the great relative size and remarkable form of their 

 skulls. In one species, for instance, the lower jaw measures 21 inches in length, 

 and is of extraordinary massiveness; while in another, although shorter, this 

 massiveness is still more exaggerated. The skull is characterised by the great depth 

 and compression of the upper mandible of the beak, which terminates in a descending 



SIDE VIEW OF SKDLL OF GIANT FUGHTLESS PATAGONIAN BIRD {PhOTOrhochis) 



(alx>ut 2 nat. size). (I<Vom Ameghino.) 



hook, towards which the extremity of the lower mandible gently ascends. The nasal 

 apertures (N) are pierced very high up on the sides of the skull, and have no partition 

 between them, and the lower mandible is truncated posteriorly, and has its two 

 branches united by a very long symphysis. A feature in which these birds differ from 

 the ostrich group is to be found in the circumstance that the quadrate-bone (Q) 

 articulates with the rest of the skull by two heads at its upper extremity, as in 

 ordinary flying-birds. In the leg-bones the tibia has a bony bridge at its lo^er 

 end for the protection of the extensor tendons, and the first toe was generally 

 present. Although well-developed wings were retained, these were useless for 

 flight; but the metacoracoid was of the elongated form characteristic of flying- 

 birds, and thus markedly different from the corresponding bone of the ostrich 

 group. The leg-bones of these birds indicate two well-marked generic types, in 

 one of which the legs were long and slender, while in the other they were more 

 massive and relatively shorter ; the former type being known as Phororhachis and 

 the latter as Brontornis. Corresponding differences obtain in the form and pro- 

 portions of the beak. Whatever be the exact serial position of these marvellous 

 birds (all of which may be included in the single family Phororhachidw), it is 



