PERFECT JOINTS 



321 



the concavity of his legs astride, from side to side, and 

 the convexity of his seat, from before backwards. 



The metacarpal bone of the thumb is articulated with 



Fio. 98. — A Section of the Hip-joint taken through the acetabulum 

 OR Articular Cup of the Pelvis and the middle of the head and 

 NECK of the Thigh-bone. 



L.T, Ligamentum teres, or round ligament. The spaces marked with 



an interrupted line ( ) represent the articular cartilages. The cavity 



of the synovial membrane is indicated by the dark line between these, 

 and, as is shown, extends along the neck of the femur beyond the limits 

 of the cartilage. The peculiar shape of the pelvis causes the section to 

 have the remarkable outline shown in the cut. This will be intelligible 

 if compared with Fig. VI. in the plate. 



the bone of the wrist, called trapezium, by a double hinge- 

 joint. _ 



A pivot-joint is one in Avhich one bone furnishes an 

 axis, or pivot, on which another turns ; or itself turns on 



