. The structure and life of birds . e lizards. Indeed it outdoes even the supple-ness of the snake. If you hold up a snake by histail, he tries to get at your hand, with a view tobiting you if he is of a poisonous kind, by bendingupward sideways. He has not much power ofhollowing his back, so as to rise without a curve tothe side. True, some snakes have much more supple-ness in an upward and downward direction than the Hooded Snake is irritated, he raises the fore partof his body so that it forms a double curve or S even he cannot make by a long way so decidedan 3 as a long
. The structure and life of birds . e lizards. Indeed it outdoes even the supple-ness of the snake. If you hold up a snake by histail, he tries to get at your hand, with a view tobiting you if he is of a poisonous kind, by bendingupward sideways. He has not much power ofhollowing his back, so as to rise without a curve tothe side. True, some snakes have much more supple-ness in an upward and downward direction than the Hooded Snake is irritated, he raises the fore partof his body so that it forms a double curve or S even he cannot make by a long way so decidedan 3 as a long-necked bird, and the reason is that inthe bird the bones which form the neck articulatewith each other differently, by a joint which is amarked improvement on the reptiles joint. The SKELETONS OF BIRD AND REPTILE 23 latter is a ball-and-socket. At the hinder end of eaclivertebra there is a protuberance, rounded on its upperside but nearly flat below, which fits into a hollow inthe vertebra behind. The fact that the protuberance is. Fig. 7.—(A) Two vertebrae of Snake. (/?) Two neck of Eagle. I. Anterior end. II. Posterior. b, ball ; cr, cervical rib; sd. saddle ; sk, socket; sf, spine ; va, tunnel through which vertebral artery passes. not a perfect ball but has its underside flattened limitsthe freedom of movement, and, in addition to this, eachvertebra bears a spine (SP, fig. 1) upon the top, the spineof one being very near to that of the next, and thusa further limit is put to movement up and down. The 24 THE STRUCTURE AND LIFE OF BIRDS CHAP. joints in a birds neck resemble two saddles laidcrosswise one upon the other, so that the pommelsof one face at right angles to those of the other, theupper saddle being, of course, upside down. In thebirds neck the saddles are so arranged that at thehinder end of each vertebra the pommels are at thetop and bottom, while at the front end they are atthe sides. Thus the two vertebrae will slide overone another sideways, or up
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