59 



spring through the air, the following muscles are employed in flexing 

 the several joints, so as to have them in readiness for another spring as 

 soon as the foot touches the ground. 



I.— Muscles flexing the Thigh upon the Axis of the Body. 



1. Sartorius, 18-00 



2. Iliacus, J S 7S 



II. The flexure of the leg upon the thigh seems to be effected 



by the vis inertia of the former, when the latter is drawn up towards 

 the body in the spring. 



HI, — Muscles flexing the Metatarsus upon the Leg. 



3. Tibialis auticus, 8 '75 



4. Extensor digitorum communis, ... 5 '25 



14-00 



' From this it would appear that the mo- 

 ments of the muscles flexing the joints 

 of the limb, during the spring, are repre- 

 sented by 33*75 oz. 



This is a small amount of force com- 

 pared with that employed in extension, 

 and in propelling the body forwards ; but 

 the flexor muscles are aided by inertia, and 

 by a special contrivance in the heel joint, 

 that remains to be described. 



The articulating surfaces of the bottom 

 of the tibia and top of the metatarsus, or 

 cannon bone, are so formed, that it is easier 

 to flex the joint forwards than backwards. 

 This is effected by making the anterior 

 curvature more rapid than the posterior 

 curvature, which produces what connois- 

 seurs in horses would call a beautiful 

 " gig action;" and this natural disposition 

 of the joint is further aided by two ad- 

 mirably contrived check ligaments, shown 

 in Figs. 11, 12, which render the motion 

 forwards much easier than that back- 

 wards. 



In Fig. Ill have shown the tendons 

 of M, gastrocnemius and M. solceus ; and 

 in Fig. 12, the tendons of the flexores di- 



NNEE SIDE OF LEFT HEEL OF 

 OSTKICH. 



Tendon of tibialis anticus. 



extensor digitorwn 



communis, 

 gastrocnemius, 

 solceus. 



acquired in running up to the point of starting; and the whole art of long jumps re- 

 solves itself into jumping vertically with a velocity equal to the acquired horizontal 

 velocity, and making both quantities a maximum. 



