492 STRUCTURE AND CLASSIFICATION OF BIRDS 



three bones do not fuse posteriorly ; the pectineal process is 

 large. 



There are at most faint traces of a ploughshare bone. 



In Cryptunis the clavicles come into contact with the 

 acrocoracoid and the scapula, but not with the small pro- 

 coracoid. 



The two coracoids are not nearly in contact at their 

 articulation with the sternum. 



The only birds with which the tinamous have been com- 

 pared are the ostrich tribe, the gallinaceous birds, rails, 

 bustards, and some of the Limicolse. PAEKEE saw in the 

 tinamou a ' cock ostrich mule ; ' and perhaps the prevalent 

 opinion is that they lie on the confines of these tw T o groups- 

 It is unquestionably to the Struthiones that they show the 

 greatest numbsr of important likenesses, 1 so much so, indeed, 

 that their inclusion in one great group with them would be 

 by no means an unreasonable way of disposing of them. 

 The salient points of resemblance are by no means confined 

 to the skeleton, but the most numerous resemblances are in 

 that part of the body of the birds. The skull, with its 

 ' dromseognathous ' palate, is strikingly like. The appearance 

 of the ethmoid as a median ossification of the skull roof is 

 struthious, but it also occurs, though not so markedly, in 

 Galhts and (according to SELENKA) in the CaprimulgidEe. It 

 is very conspicuous in the tinamou and the Struthiones. The 

 open pelvis is especially like that of Aptenjx. The single- 

 headed quadrate is struthious ; but, as already mentioned, 

 the struthious birds are not uniform in this character. 



The sternum, with its antero-lateral and postero-lateral 

 processes, recalls that of Aptenjx, in spite of the enormous 

 length of these parts and a consequent superficial dissimi- 

 larity. The absent, or rudimentary, ploughshare bone may 

 perhaps be passed over as correlated with the imperfect 

 flight. As to the soft parts, the peculiar additional accessory 



1 A singular if less important likeness than some mentioned above has been 

 referred to by Mr. BARTLETT (' Notes on the Breeding of several Species of Birds,' 

 &c., P. Z. S. 1868, p. 114). The male Rliyncliotus rnfescens incubates, as in 

 the Struthiones, while the chick ' much resembles the young of a Rhea.'' 



