An introduction to the study of the comparative anatomy of animals . bralcolumn coincide with the principal axis, hence we havereferred to them as the axial skeleton. Let two lines bedrawn at right angles to the principal axis from the pointswhere the limbs are joined on to the body; these will be thetwo secondary axes. Let us suppose the limbs to bestraightened out along the secondary axes, as in the diagram,palms downwards. Then we find that the humerus in thearm, and the femur in the leg, correspond with the secondaryaxes. In the fore-arm the radius lies in front of the secondaryaxis, and i
An introduction to the study of the comparative anatomy of animals . bralcolumn coincide with the principal axis, hence we havereferred to them as the axial skeleton. Let two lines bedrawn at right angles to the principal axis from the pointswhere the limbs are joined on to the body; these will be thetwo secondary axes. Let us suppose the limbs to bestraightened out along the secondary axes, as in the diagram,palms downwards. Then we find that the humerus in thearm, and the femur in the leg, correspond with the secondaryaxes. In the fore-arm the radius lies in front of the secondaryaxis, and is called pre-axial; the ulna lies behind it, and is called Digitized by Microsoft® 36 COMPARATIVE ANATOMY post-axial. Similarly, in the leg, the tibia is pre-axial, thefibula post-axial. In the wrist we find a proximal row of threebones—radiale lying beyond the radius, ulnare lying beyondthe ulna, and a median bone, the intermedium, lying betweenthem. The distal row has five bones, and we begin countingfrom the pre-axial or radial side. The thumb, therefore, is. x:
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