September 2, 1897] 



NATURE 



429 



•he arrangement of the constituent parts of the skeleton be 

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

 isstead 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 decep- 

 tive. 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 con- 

 vexities. 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 longi- 

 tudinally 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 

 vertebra:, are in a stale 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 eff"orts 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 ex- 

 tension 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 extende<l, the ends are drawn further apart, the band 

 is made tense, and the ilium might in consequence be drawn 

 upon, so as to affect the inclination of the pelvis. As the liga- 

 ment 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 spince," 

 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 pull, per unit of length, of the psoae muscles attached 

 in front is greater than the average pull, per unit of length, of 

 the muscles attached behind in the same region. 



The m'iscles which lie on the back of the neck and which are 

 attached to the occipital part of the skull, when brought into 

 action, will necessarily affect the position of the head. The 

 new-born infant has no power to raise the head, which is bent 

 forward, so that the chin is approximated to the chest. As it 



NO. 1453, VOL. 56] 



acquires strength the head becomes raised by the muscles of the 

 back of the neck, and the flexible spine in the cervical region 

 loses its primary curve, concave forwards, and gradually assumes 

 the cervical convexity. The formation of this curve is, I be- 

 lieve, assisted by the anterior recti muscles, the lower ends ot 

 which are attached to the front of the vertebrae, whilst their upper 

 ends are connected to the basi-occipital. In the elevation of the 

 head the opposite ends of the muscles are drawn apart, which 

 would exercise a forward traction upon the cervical vertebrae. 

 The production of the cervical convexity precedes the formation 

 of the lumbar curve, for an infant can raise its head, and take 

 notice of surrounding objects, months before it can stand upon 

 its feet. 



We shall now look at the bones in the thigh and leg, which 

 possess characters that are distinctively human, and which are 

 associated with the erect posture. These characters can be 

 more clearly recognised when the bones are contrasted with the 

 corresponding bones of the large Anthropoid apes. 



As compared with the ape, the shaft of the human thigh bone 

 is not so broad in relation to its length ; when standing erect 

 the shaft is somewhat more oblique, it is more convex forwards 

 and generally more finely modelled, and it has three almost equal 

 surfaces, the anterior of which is convex. But, further, a strong 

 ridge (linea aspera) extends vertically down its posterior surface; 

 so that a section through the shaft is triangular, with the two 

 anterior angles rounded and the posterior prominent. In the 

 Gorilla, Chimpanzee, and Orang, the shaft is flattened from 

 before backwards, and the linea aspera is represented by two 

 faint lines, separated from each other by an intermediate narrow 

 area. A section through the shaft approximates to an ellipse. 

 In the Gibbon the femur is greatly elongated, and the shaft is 

 smooth and cylindriform. The linea aspera is for the attach- 

 ment of powerful muscles, which are more closely aggregated 

 in man than in apes, so that the human thigh possesses more 

 graceful contours. 



In the human femur the shaft is separated from the neck by a 

 strong anterior intertrochanteric ridge, to which is attached the 

 ilio-femoral ligament of the hip joint, which, by its strength 

 and tension, plays so important a part in keeping the joint ex- 

 tended when the body is erect. In the Anthropoid apes this 

 ridge is faint in the Gorilla, and scarcely recognisable in the 

 Orang, Gibbon, and Chimpanzee, and the ilio-femoral ligament 

 in them is comparatively feeble. It may safely therefore be 

 inferred that in apes, with their semi-erect, crouching attitude, 

 the ilio-femoral band is not subjected to, or capable of sustaining, 

 the same strain as in man. 



The head of the thigh bone is also distinctive. In the 

 apes the surface covered by cartilage is approximately a 

 sphere, and is considerably more than a hemisphere. It is 

 sharply differentiated from the neck by a definite boundary, 

 and it has a mushroom-like shape. In man the major part of 

 the head is also approximately a sphere ; but, in addition, there 

 is an extension outwards of the articular area on the anterior 

 surface and upper border of the neck of the bone. The form ot 

 this extended area differs from the spherical shape of the head 

 in general. The curvature of a normal section of its surface 

 has a much larger radius than the curvature of a normal section 

 of the head, near the attachment of the ligamentum teres. 



The amount of this extended area varies in different femora, 

 but as a rule it is larger and more strongly marked in Europeans 

 than in the femora of some savages which I have examined. 

 When the joint is in the erect attitude, the area is in contact with 

 the back of the iliac part of the ilio-femoral ligament. It 

 provides a cartilaginous surface which, during extension of the 

 joint, is not situated in the acetabulum, but, owing to the centre 

 of gravity falling behind the axis of movement, is pressed against 

 that ligament, and contributes materially to its tension. It is 

 associated with the characteristic position of the human hip 

 joint in standing, and may be called appropriately the extensor 

 area. When the femur is abducted it passes within the acet- 

 abulum. The head of the femur in man is not so sharply 

 differentiated from the neck as in the Anthropoid apes, especially 

 in the region of the extensor articular area. 



Both man and apes possess at the lower end of the femur a 

 trochlear or pulley like surAice in front for the patella, and two 

 condyles for the tibia. In the apes the trochlea is shallow, and 

 the concave curve from side to side is a segment of an approxi- 

 mate circle, with a large radius. In man the trochlea is much 

 deeper, and the inner and outer parts of the curve deviate con- 

 siderably from a circle, and are not symmettical ; the outer part 



