INTRODUCTION. 



23 



arch, and renders it capable of supporting the weight of the 

 body in standing, leaping, and in falling from considerable 

 altitudes. 



Joints. — Where the limbs are designed to move to and 

 fro simply in one plane, the ginglymoid or hinge-joint is ap- 

 plied ; and where more extensive motions of the limbs are 

 requisite, the enarthrodial, or ball-and-socket joint, is intro- 

 duced. These two kinds of joints predominate in the locomo- 

 tive organs of the animal kingdom. 



The enarthrodial joint has by far the most extensive power 

 of motion, and is therefore selected for uniting the limbs to the 

 trunk. It permits of the several motions of the limbs termed 

 pronation, supination, flexion, extension, abduction, adduc- 

 tion, and revolution upon the axis of the limb or bone about a 

 conical area, whose apex is the axis of the head of the bone, 

 and base circumscribed by the distal extremity of the limb."-"- 



The ginglymoid or hinge-joints are for the most part spiral in 

 their nature. They admit in certain cases of a limited degree of 

 lateral rocking. Much attention has been paid to the subject 

 of joints (particularly human ones) by the brothers Weber, 

 Professor Meyer of Zurich, and likewise by Langer, Henke, 

 Meissner, and Goodsir. Langer, Henke, and Meissner suc- 

 ceeded in demonstrating the " screw configuration" of the 

 articular surfaces of the elbow, ankle, and calcaneo-astraga- 

 loid joints, and Goodsir showed that the articular surface 

 of the knee-joint consist of " a double conical screw combina- 

 tion." The last-named observer also expressed his belief 

 " that articular combinations with opposite windings on 

 opposite sides of the body, similar to those in the knee-joint, 

 exist in the ankle and tarsal, and in the elbow and carpal 

 joints ; and that the hip and shoulder joints consist of single 

 threaded couples, but also with opposite windings on oppo- 

 site sides of the body." I have succeeded in demonstrating 

 a similar spiral configuration in the several bones and joints 

 of the wing of the bat and bird, and in the extremities of 

 most quadrupeds. The bones of animals, particularly the 

 extremities, are, as a rule, twisted levers, and act after the 

 manner of screws. This arrangement enables the higher 



1 Bishopj op. cit. 



