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 Stereornithes, as they are called, certainly cannot be included among the 
modern flightless group of giant birds, and it is uncertain whether they can claim 
a place with the preceding orders in the great subclass of Carinate ; 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 SKULL OF GIANT FLIGHTLESS PATAGONIAN BIRD (Phororhachis) 
(about 2 nat. size). (From Ameghino.) 
hook, towards which the extremity of the lower mandible gently ascends. The nasal 
apertures (V) 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 (() 
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 lower 
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 Phororhachide), it is 
