STRUCTURE OF THE HUMAN BODY 27 



small things with great, the giant Atlas was supposed to bear the 

 globe on his shoulders. This vertebra presents two shallow cups 

 on the side facing the skull, from which project two corresponding 

 rounded projections. A hinge -joint is thus constituted, as a result 

 of which we are able to nod our heads backwards and forwards. 

 Movement from side to side would, however, be restricted by this 

 arrangement if it were not for another one which exists to com- 

 pensate it. The second vertebra, or axis, bears a firm bony peg, 

 which projects through the ring -like atlas towards 

 its ventral side and forms, 



A. 



as its name indicates, a pivot 

 round which the head with 

 the atlas can turn, too great 

 freedom of movement being Fig 6 _ A> Atlas vertebra> anterior vieWT ventral surfac " e up _ 



fl rm fihrm !<; wards: ae, body; g, cup for reception of occipital condyle;^ pro- 

 cess; k, position of a ligament; /, spinal canal. B, Axis vertebra, 



bands or ligaments which 

 run from the peg to the 

 skull. Following the neck- vertebrae come twelve rib -bearing 

 chest-vertebra, which form part of the dorsal wall of the chest- 

 cavity. Next come five large loin-vertebrce, the size of which is 

 due to the necessity for a firm support to the very considerable 

 weight of the parts of the body coming above them. Still lower 

 down this necessity becomes still greater, and the demand is met 

 by a complicated basin-shaped mass of bone, t\\epelvis, the numerous 

 arch-like curves of which are so arranged as to confer immense 

 strength. The pelvis consists of three bones firmly fused together 

 in the adult, the dorsal one, which alone belongs to the backbone, 

 being the sacrum, made up of five broad flat sacral vertebras 

 immovably fused together. The last section of the backbone is 

 a small curved structure termed the coccyx (Gk. for cuckoo), so 

 named from its supposed resemblance to a cuckoo's beak, and 

 resulting from the intimate union of four small tail vertebrae. It is 

 chiefly interesting as being the useless representative of the tail, 

 which is such a useful appendage in many of the lower forms. 



2. The Skull. The hard parts of the head together con- 

 stitute the skull (see fig. 7), which consists of a brain-case, of 

 relatively enormous size in Man, and the bony framework of the 

 face. The brain-case is made up of a number of flat bones, 

 firmly united by interlocking edges and also in part by over- 

 lapping surfaces, the net result being an arched box of very 



