466 STEUCTUEE AND CLASSIFICATION OF BIEOS 



The number of cervical vertebra ^ among the Anseres varies 

 considerably. The smallest number is found, for example, 

 in Plectropterus gambensis, Biziura lohata, and Tachyeres 

 cinereus, where there are only sixteen. In CEdemia nigra 

 there are seventeen ; among the swans, twenty to twenty- 

 four. The number of true ribs also varies considerably. 

 The smallest number is to be seen in Cereopsis, where there 

 are but five. Tachyeres, Plectropterus, and a number of 

 other genera have seven ; there are eight in Tadorna vulp- 

 anser, and as many as nine in certain swans and geese. 



The sternum, which has a moderate spina externa, but 

 no spina interna, is whole in Cnemiornis, but has two 

 notches or foramina in other Anseres. The coracoids come 

 into contact, but do not overlap at their sternal articulation. 

 The procoracoid is small, and does not reach the clavicle, 

 which, however, reaches the scapula. 



The skull has large oval sessile basipterygoid processes. 

 It is holorhinal and desmognathous. There are frequently 

 lateral occipital fontanelles, as in many ' pluvialine ' birds.^. 

 The palatines are remarkable for the rudimentary character 

 of their inner laminae, which brings about a resemblance to 

 the gallinaceous birds, as has been pointed out by Huxley, 

 and, it may be added, to the parrots. That part of the 

 palatine is only indicated by a not well marked ridge which 

 is totally absent in Bernicla leucopsis, Chen ccerulescens. 

 The general direction of the bone, therefore, is oblique ; it is 

 only near to the attachment with the pterygoids that it 

 becomes feathered out in a horizontal direction. That, at 

 least, is the more normal arrangement ; for in Mergus the 

 greater part of the bone has its upper and lower surface co- 

 incident with the horizontal axis. This, too, is the case with 

 Biziura lobata. 



The oval basipterygoid facets for articulation with the 



■ For osteology see Paekee, ' On the Morphology of the Duck and the Auk 

 Tribes,' Cunningham Memoirs B. Irish Ac. No. 6, 1890, and Shufeldt, ' On N. 

 American Anseres,' P. U. S. Nat. Mus. xi. p. 215. 



' Absent in Cereopsis, Biziura, Cygnus, and Cnemiornis. See Owen, Tr. Z. 

 8. ix. pt iii. 



