260 Observations upon the Affinities 



the members of this sub-class are strictly monogamous ; the 

 sexes incubating by turns, and assisting to rear their broods. 

 There is no ascertained instance of a truly polygamous bird, 

 save among the Gressores. 



Of course, the Accipitres, (Linnaeus), being admitted into 

 this great primary division, compose an exceedingly distinct 

 ordinal section of it. Another, equally so, has never, that I 

 am aware of, been definitively recognised, (unless by L'Her- 

 minier in his excellent work on the sterna of birds, where it 

 is partially indicated). It consists of that excessively nume- 

 rous group of species which are distinguished by possessing 

 five pairs of muscles to the inferior larynx ; all of which a- 

 gree most closely in the structure of the skeleton, in that of 

 the digestive organs, and, in short, in all the principal details 

 of their anatomy. The members of this group accord in their 

 rudimental structure, however in their adaptive characters 

 they may vary exceedingly. The swallow and the tree-creep- 

 er, the promerops, the finch, and the crow, the dipper and 

 the manakin, are merely so many modifications of a single 

 anatomical type, to which no species that does not possess 

 the complex vocal apparatus before adverted to, appertains. 

 Every member of this most distinctly demarcated group, may 

 be at once recognised by the conformation of its sternal ap- 

 paratus ;* and, except from the diurnal Accipitres, by the 

 constant presence of two small ccecal appendages to the in- 

 testine, whereas all other Insessores, so far as my researches 

 have gone, are either entirely destitute of cceca, or have them 

 developed to the same proportional magnitude as in the owls, 

 which, throughout the present sub-class, is never exceeded. 

 The absence of cooca I have ascertained in the hombills, king- 

 fishers and halcyons, toucans, touracos, parrots, woodpeck- 

 ers, wrynecks, piculets, (Picumnus), swifts, and humming- 

 birds ; and their presence, of the maximum dimensions stated, 

 in the todies, jacamars, trogons, cuckoos, (including Scy- 

 throps), and moth-hunters, (Caprimulgidce) : judging from 

 analogy, I infer that they are absent in the hoopoes, bee-eat- 

 ers, rollers, barbets, honey-guides, and perhaps motmots, and 

 the Oxyrhynchus ; and developed in the puff-birds, courols, 

 coucals, malkohas, and ani. Information relative to the 

 anatomy of either of the twelve last-named groups, would to 

 me be extremely acceptable. 



* Several examples of this type of sternum, with the other bones in im- 

 mediate connexion with it, are depicted in Mr. Yarrell's ' History of British 

 Birds,' as vignettes to the descriptions of some of the thrushes, and allied 

 genera. 



