Wymaii.] 252 [Juuo 5, 



soles and palms. The an;;le formed In the limbs corresponds with the 

 elbows and the knees, and thus marks off fore arms and legs Irom arms 

 and thighs, these last being very short. Thirdly, during the stage just 

 mentioned, both upper arms and thighs projected at right angles from 

 the sides of the body. They now begin to change their direction with 

 reference to the trunk, but in a perfectly symmetrical manner. The 

 elbow which has thus far projected outwards, now swings backwards 

 to the side of the; thorax, and the knee forwards towards the side of 

 the abdomen. This condition of things is readily seen in a human 

 embryo in the writer's collection, measuring 0.60 inch in length, and 

 represented in Fig. 5. The effect of this change of position would be 

 to make the palms face forwards, and it 

 makes the soles face partly back-wards. 

 This tendency, however, as regards the 

 hand, is counteracted by a remarkable 

 change of position in the fore arm. This 

 is slowly rotated inwards, so that the palm 

 is made to face almost backwards. In 

 those animals which walk on the palms 

 pj„ 5 of their hands, the hand is bent on the 



fore arm, so that its back is raised, the jJalm 

 directed more or less downwards, and thus the limb is adapted to walk- 

 in"- or crawling. At the same time a similar change takes place in 

 the feet, the backs of which are raised towards the fore part of the 

 leo-, and the toes directed forwards, and the sole downwards. The 

 rotation of the fore arm just mentioned is the chief cause of the inter- 

 ference -\vith the symmetry of the limbs ; were it not for this the hands 

 and feet would have assumed exactly symmetrical attitudes, the toes 

 projecting forwards and the fingers backwards, the back of the foot 

 looking towards the fore part of the leg, and the back of the hand 

 towards the hind part of the fore arm. 



If we admit the' idea of symmetry in structure between arms and 

 legs, and would compare the movements of the two in man and ani- 

 mals, we must change in some respects the terms flexion and extension, 

 from those ordinai-ily used in the description of the human body. We 

 Avill suppose the human skeleton suspended with the vertebral column 

 horizontal, the limbs slightly flexed, the toes and fingers pointing 

 downwards, the palms facing forwards and the soles backwards. Flex- 

 ion of the humerus would be back->vards, of the femur forwards ; of the 

 fore arm forwards, of the leg backwards ; of the hand backwards, that 

 is by carrying the back of it towards the back of the fore arm, and 

 the foot forwards. Thus the movements would be symmetrical through- 

 put in the two limbs. Supposing the limbs to be of equal strength, 

 somew'.iat flexed, the soles and palms resting on the ground, they 



