1856.] OWEN GASTORNIS PARISIENSIS. 211 



leave no space answering to the intercondyloid one in Aptornis, 

 Notornis, &c. ; but the continuous surfaces form a ridge which 

 bounds below the supracondyloid space, the same being bounded 

 above by the ridge extending outwards from the supratendinal 

 bridge, e. This is nearer the inner side of the bone, is subtransverse, 

 rather narrow, with a widely elliptical lower outlet opening above 

 the inner condyle : the canal (/) leading to the bridge has an internal 

 boundary ridge : a shallow longitudinal groove divides the outer side 

 of the bridge from a tuberosity above the outer condyle. The under 

 and hinder parts of the trochlear surface are concave transversely. 



In the Ostrich {Struthio camelus) the breadth and depth of the 

 condyles are equal : they are less produced anteriorly than in other 

 birds, and their articular surfaces are so continuous as to leave no 

 well-defined intercondyloid space ; that surface projects in a trans- 

 verse concave line some way in advance of the supracondyloid space, 

 which is marked by a submedian transverse ridge or broad tubercle, 

 external to which is a rounded depression. There is no supratendinal 

 bridge or groove. The under trochlear surface is broad and shghtly 

 concave from side to side ; posteriorly it is deepened by the develop- 

 ment of its borders, of which the inner one is the sharpest and most 

 suddenly produced. This surface is traversed by a slight median 

 longitudinal rising. The ectocondyloid surface is concave, and has a 

 pit fitting the end of a finger. The entocondyloid surface shows a 

 deep pit near its anterior part, whence a wide groove curves back- 

 wards, becoming broader and shallower to the posterior part of the 

 condyle. The distal condyles expand more suddenly beyond the 

 shaft than in most birds. 



Order Natatores. 



In the Swan {Cygnus ferus) the breadth and depth of the con- 

 dyles are equal: the intercondyloid space, fig. 13, a, exceeds either con- 

 dyle : it has a very shallow transverse fossa. The bridge, e, of mode- 

 rate breadth, is median, transverse, and straight ; it spans a wide and 

 deep canal, the lower aperture of which looks forwards and opens 

 immediately above the intercondyloid space. The canal leading to 

 the bridge has no lateral sharp ridge : the inner border is most 

 developed and is rounded. The under and hinder trochlear surface 

 is very slightly concave transversely. Both ecto- and ento-condyloid 

 surfaces are flat. 



I have received from the brick-earth at Grays, in Essex, the lower 

 end of a fossil tibia (figs. 13 «, 13 5) corresponding precisely in the 

 modifications of its distal end with those of the Cy gnus ferus : it is 

 very little larger than the tibia of the Wild Swan, and may be of the 

 same species. The bone had undergone the same change as the bones of 

 the Elephas primigenius. Rhinoceros tichorhinuSi &c., from the same 

 formation. 



The above characters are very closely repeated in the Goose 

 {Anser palustris) : the bridge is broader in proportion to the size of 

 the canal. The under surface of the trochlea has a feeble median 



