DIVISIONS OF THE CLASS AYES. 239 



finest Pheasants in the world, the Impeyan Pheasant from the Himalayas, the Tragopans, and the 

 Lobed Pheasant of Borneo being most beautiful creatures. Lastly, between the islands of Bali and 

 Lombok passes a deep sea boundary called " Wallace's line," which divides the Australian region from 

 the Indian, and although these islands lie so close together, the great depth of the channel between 

 them seems to mark them out as frontier lines of two ancient continents. Certain it is that the birds 

 and animals on each side of Wallace's line differ remarkably; and the Australian region, which 

 includes all the Moluccas, New Guinea, and Oceania, in addition to the Australian continent 

 and New Zealand, presents us with forms not found elsewhere, such as Birds of Paradise, Casso- 

 waries, Lyre-birds, and a large variety of peculiar types. Many smaller divisions of the globe are 

 now recognised, but the above are the main ones, which may occasionally be referred to in these 

 pages.* 



Many birds migrate, and the student of migration alone would find sufficient material there for 

 the work of a lifetime ; and it seems almost impossible to account for the instinct or other causes 

 which bring birds regularly year by year to breed in the same haunts, and which drive them 

 away at the same change of season. Why is it, for instance, that species of similar habits and 

 form, and both visiting Europe in equal abundance, should occupy such different winter quarters? 

 Yet the common Red-backed Shrike, or Butcher-bird (Lanius collyrio), when he is said to 

 leave Europe, passes by the Nile Valley along the east coast of Africa down to the Cape, where he 

 brings up a second brood of nestlings ; while the Wood-Chat Shrike (Lanius auriculatus), a bird of 

 about the same size and of precisely similar habits, proceeds down the Nile Valley and invades Abys- 

 sinia in the winter, and also occupies Senegambia, where a Red-backed Shrike has never been found 

 yet by a naturalist. Nothing whatever is known by which route the bird gets to the Gambia: 

 whether he follows the same one as his red-backed relation as far as Abyssinia, and then skirts the 

 southern edge of the Sahara, or whether he reaches north-western Africa by a direct flight across the 

 Great Desert. Many other such problems in the economy of our most familiar species are still 

 awaiting further scientific research. 



CHAPTER II. 

 THE ANATOMY OF A BIRD.f 



The Three Divisions of the Class Aves ANATOMY OF A BIRD The Skeleton Distinctive Features - Peculiar Bone Character 

 The Skull - Difference between the Skull of Birds and that of Mammals The Jawbones Vertebral Column 

 Sternum Fore limbs Hind limbs Toes The Muscular System How a Bird remains Fixed when Asleep- The Oil- 

 gland The Nervous System The Brain The Eye The Ear The Digestive System The Dental papillae The 

 Beak Tongue - Gullet Crop Stomach Uses of the Gizzard Intestine The Liver, Pancreas, and Spleen The Blood 

 and Circulatory System Temperature of Blood of a Bird Blood Corpuscles The Heart The Kespiratory System 

 Lungs Air-sacs The Organs of Voice The Egg Classification of the Class Aves. 



BIRDS may be separated into three great divisions : the Carinatce, or birds with a keeled sternum, the 

 Ratitce, or birds having a raft-like sternum, and the Saururce, or lizard-like birds. The last of 

 these orders links the birds with the reptiles, and does not concern us here, as it contains only one 

 genus, and that a fossil one, the Archwopteryx lithographica, respecting which a few words will be 

 found at the end of this article (Vol. IV, pp. 236-8). The other two divisions are of great 

 importance, and are easily recognisable, although the characters which separate them are chiefly 

 anatomical. The principal point of difference lies in the sternum, or breast-bone, and the name 

 Carinatce is given to all those which have a keel (carina) or sternal ridge largely developed, as in the 

 common fowl ; and this is present in the great majority of birds. The Ratitce have not got this keel, 

 and in this division are found the Struthious birds Ostriches, Cassowaries, <fcc. They are all species 

 which cannot fly ; and although the number at present existing is small, the fact of their being found 



* Dr. Sclater, F.R S., originated, in 1858, this scheme of the six zoogeographical divisions of the globe, 

 f In the preparation of this chapter, the author begs to acknowledge the assistance he has received from his friend 

 Professor F. Jeffrey Bell, B.A. 



