Finally, let us sum up the more important modifications which domestic rabbits have undergone, together with their causes as far as we can obscurely see them. By the supply of abundant and nutritious food, together with little exercise, and by the continued selection of the heaviest individuals, the weight of the larger breeds has been more than doubled. The bones of the limbs have increased in weight (but the hind legs less than the front legs), in due proportion with the increased weight of body; but in length they have not increased in due proportion, and this may have been caused by the want of proper exercise. With the increased size of the body the third cervical vertebra has assumed characters proper to the fourth cervical; and the eighth and ninth dorsal vertebræ have similarly assumed characters proper to the tenth and posterior vertebræ. The skull in the larger breeds has increased in length, but not in due proportion with the increased length of body; the brain has not duly increased in dimensions, or has even actually decreased, and consequently the bony case for the brain has remained narrow, and by correlation has affected the bones of the face and the entire length of the skull. The skull has thus acquired its characteristic narrowness. From unknown causes the supra-orbital processes of the frontal bones and the free end of the malar bones have increased in breadth; and in the larger breeds {130} the occipital foramen is generally much less deeply notched than in wild rabbits. Certain parts of the scapula and the terminal sternal bones have become highly variable in shape. The ears have been increased enormously in length and breadth through continued selection; their weight, conjoined probably with the disuse of their muscles, has caused them to lop downwards; and this has affected the position and form of the bony auditory meatus; and this again, by correlation, the position in a slight degree of almost every bone in the upper part of the skull, and even the position of the condyles of the lower jaw. * * * * * {131} CHAPTER V. DOMESTIC PIGEONS. ENUMERATION AND DESCRIPTION OF THE SEVERAL BREEDS--INDIVIDUAL VARIABILITY--VARIATIONS OF A REMARKABLE NATURE--OSTEOLOGICAL CHARACTERS: SKULL, LOWER JAW, NUMBER OF VERTEBRÆ--CORRELATION OF GROWTH: TONGUE WITH BEAK; EYELIDS AND NOSTRILS WITH WATTLED SKIN--NUMBER OF WING-FEATHERS, AND LENGTH OF WING--COLOUR AND DOWN--WEBBED AND FEATHERED FEET--ON THE EFFECTS OF DISUSE--LENGTH OF FEET IN CORRELATION WITH LENGTH OF BEAK--LENGTH OP STERNUM, SCAPULA, AND FURCULA--LENGTH OF WINGS--SUMMARY ON THE POINTS OF DIFFERENCE IN THE SEVERAL BREEDS