TRANSACTIONS OF SECTION H. 775 



flesh be removed, and the arrangement of the constituent parts of the skeleton be 

 studied, it will be seen that the axis of the spine in them, instead of being vertical 

 is oblique, and that there is no proper lumbar convexity ; that the hip and knee 

 joints, so far from being extended, are bent ; that the thigh is not in the axis of 

 the spine, and that the leg, instead of being in a vertical line with the thigh, is set 

 at an acute angle to it. The so-called vertical attitude therefore in these 

 animals is altogether deceptive. It does not approximate to, and can in no sense 

 be looked upon as equivalent to, the erect attitude in man. 



We may now consider what agents come into operation in changing the curve 

 of the spine from the concavity forwards, found in the new-born infant, to the 

 alternating series of curves so characteristic of the adult. The production of the 

 lumbar convexity is, without doubt, due to structures associated with the spine, 

 the pelvis and the lower limbs, whilst the cervical convexity is due to structures 

 acting on the spine and the head. 



There can, I think, be little doubt that muscular action plays a large part in the 

 production of the cervical and lumbar convexities. The study of the muscles, 

 associated with and connected to the spinal column, shows that large symmetrically 

 arranged muscles, many of which are attached to the neural arches and transverse 

 processes of the vertebrae, extend longitudinally along the back of the spine, and 

 some of them reach the head. On the other hand, those muscles which lie in 

 front of the spine, and are attached to the vertebrae, are few in number, and are 

 practically limited to the cervical and lumbar regions, in which the spine acquires 

 a convexity forwards. 



It has already been pointed out that the formation of the lumbar convexity is 

 correlated with the power of extending the hip joints and straightening the 

 lower limbs. When these joints are in the position of extension, an important 

 pair of muscles called the 'psoae,' which reach from the small trochanter of the femur 

 to the bodies and transverse processes of the lumbar vertebrae, are in a state of 

 tension. In the act of extending the hip joints so as to raise the body to the erect 

 position, the opposite ends of these muscles are drawn asunder, and the muscles are 

 stretched and elongated, so that they necessarily exercise traction upon the 

 lumbar spine. Owing to its flexibility and elasticity, a forward convexity is in 

 course of time produced in it in this region. By repeated eflbrts the convexity 

 becomes fixed and assumes its specific character. 



Along with the changes in the spinal column, a modification also takes place 

 in the inclination of the pelvis during the extension of the hip joints and the 

 straightening of the lower limbs. The muscle called ' iliacus ' is conjoined with 

 the psoas at its attachment to the small trochanter, but instead of being connected 

 to the spinal column by its upper end, it is attached to the anterior surface of the 

 ilium. It exercises traction therefore on that bone, draws it forwards and increases 

 the obliquity of the pelvic brim. This in its turn will react on the lumbar spine 

 and assist in fixing its convexity. 



By some anatomists great importance has been given to the ' ilio-femoral band,' 

 situated in the anterior part of the capsular ligament of the hip joint, as causing 

 the inclination of the pelvis, and in promoting the lumbar curve. This band is 

 attached by its opposite ends to the femur and the ilium. As the hip joint is being 

 extended, the ends are dravm further apart, the band is made tense, and the ilium 

 might in consequence be drawn upon, so as to aiTect the inclination of the pelvis. 

 As the hgament has no attachment to the spinal column, it cannot draw directly 

 on it, but could only affect it indirectly through its iliac connections. It can 

 therefore, I think, play only a subordinate part in the production of the lumbar 

 curve. 



Contemporaneous with the straightening of the lower limbs and the extension 

 of the hip joints, the spinal column itself is elevated by muscles of the back, 

 named ' erectores spinae,' which, taking their fixed points below, draw upon the 

 vertebrae and ribs and erect the spine. The lumbar convexity is the form of stable 

 equilibrium which the flexible spinal column tends to take under the action of 

 the muscular forces which pull upon it in front and behind. It is probably due to 

 the fact that the average puU, per unit of length, of the psoae muscles attached in 



