22 ANATOIMY OF VERTEBRATES. 



other across the midline in some GrallcG {Ardea) ; and in a slight 

 degree in some diurnal Raptores. The borders of the coracoid 

 grooves show modifications characteristic of genera and species.^ 

 In the Albatross the coracoid grooves extend to the outer ano'les 

 of the sternum, between li and s, fig. 13. In most Birds with 

 a like extent of groove the upper or inner border is developed 

 behind and beyond it into a ^ costal process : ' but the coracoid 

 grooves do not reach the outer angle in many Birds, and the 

 angle itself is then j)roduced to form the process, figs. 15, 19 and 

 20, d. It is long and slender in some Rasores {Perdix) ; short 

 and broad in most Raptores : but, in many birds it is represented, 

 as in the Eagles, merely by the angle between the anterior and 

 costal borders. On an average about half of the lateral margin 

 of the sternum is adapted for articulating with the dorsal htema- 

 pophyses, figs. 13, h d and 15, h: but, when the sternum is long, 

 the ' costal border,' fig. 15, c, is shorter; and when the sternum is 

 short it occupies a larger extent of the lateral margin. The part 

 of the bird's sternum answerino; to that of Mammals is included 

 between the costal borders, fig. 16, c, c : the rest corresj^onds with 

 the ' xiphoid ' prolongation. Thus the Apteryx, Emeu, and Ostrich 

 most resemble Mammals in the projoortions of the costal and non- 

 costal parts of the sternum ; whilst in most birds of flight the non- 

 costal part, fig. 15, a,f, extends along that part of the great visceral 

 cavity, which would be similarly defended were the xiphoid car- 



m X 



Skeleton of the Topaz Humming Bird ir>'oclnlus Pella, Cuv.). 



tilage to be produced and expanded in the same degree in Man. 

 In the Crocodile, where it is so produced, without expanding, 



' The value of these and other sternal characters in Palfeontology may be estimated 

 by reference to my 'British Fossil Mammals and Bird?,' p. 549 {Lithornis), and p. 

 236 {Cahhates). 



