256 ELEMENTS OF ORNITHOLOGY, 
jaw joins the skull by the intervention of aquadrate bone. The 
right auriculo-ventricular valve of the four-chambered heart is 
muscular, and there is a single aortic arch which arches over the 
right bronchus. The optic lobes of the brain are lateral and 
depressed, and reproduction is in all cases oviparous. 
We put forward, in our initial chapter, a sketch which we 
hoped might serve as an introduction to the whole Class of Birds. 
But in our treatment of the subject we deliberately adopted 
modes of grouping which we thought might be acceptable to 
the beginner, and which had spontaneously suggested themselves 
to the first teachers and classifiers of our science. 
Now that we have, however, made acquaintance with the 
anatomy of Birds, the time has come to put away the notions 
wherewith we began, in favour of more advanced views. 
We spoke’ of Pigeons immediately after Fowls and Phea- 
sants, and of such they were formerly regarded as allies; but 
now the study of anatomy has separated these groups widely. 
We treated * of the Penguin in connection with the Auk, for at 
first sight these erect flightless Birds present obvious resem- 
blances. Advanced Ornithology, however, places them poles 
asunder. Close after the Cormorants we have spoken of * those 
yet more familiar coast-birds, the Gulls, and after them the 
Petrels ; but we shall see that there is no real affinity between 
them, though they at first seem alike. Neither has the Frigate- 
bird any close relationship with the Albatross. The Flamin- 
goes and the Herons, the Storks and the Cranes naturally seem 
to the beginner akin, but they must be widely separated by the 
advanced student, and the Horned Screamer of the South- 
American forests will by him be brought down to the level of 
the Goose. 
The Curlew and the Ibis*, with their long bills, look alike, 
but mature study shows us that the Curlew is a Plover ; while 
Coursers and the Tinamous’, however to the popular eve they 
may seem to run in couples, are seen by the scientific observer 
to have hardly anything in common save their bird-nature and 
mode of locomotion. However like to an ordinary Plover a 
Stone-curlew (Cdicnemus) may look, it turns out in reality to 
be far more of a Bustard. 
For the sake of the beginner, we have mentioned ° the stream- 
1 See ante, p. 12. Pep toa, Sip 28: 
4 See ante, p. 53. 5 Pp. 50 & 51. & P. 69. 
