832 OF THE STRUCTURE AND FUNCTIONS OF MUSCULAR TISSUE. 



maxima terminate tangentially. M. Carlet, 1 who has lately bestowed much 

 attention on the movements of locomotion in man, divides each step into two 

 parts one, during which both feet are in contact with the ground (temps du 

 double appui), and the other when the body is supported by one foot alone 

 (temps de I'appui unilateral). A. Period of Double Contact. 1. At the be- 

 ginning of the period of double contact, when the foot in front only touches 

 the ground with the heel, the posterior leg is stretched, and rests only on the 

 extremities of the metatarsal bones and the phalanges. The knee of the 

 front leg is extended or slightly flexed. The bicotyloidean axis is oblique, 

 from before backwards, and from above downwards. The trunk descends at 

 the same time that its lateral and forward inclination diminishes. The pubis 

 is turned towards the side of the posterior leg. 2. In the middle of the period 

 of double contact, that is to say when the front foot begins to touch the ground 

 along its whole length, the posterior leg only touches it with its phalanges. 

 The knee of the fore leg is rather more bent. The position of the bicoty- 

 loidean axis is the same as before. The trunk has gained its lowest position. 

 The pubis is situated above the axis of the path to be pursued. 3. At the 

 end of the period of double contact, that is when the posterior leg only 

 touches the ground by the ends of its phalanges, the front leg has begun to 

 extend the knee-joint. The bicotyloidean line is oblique as before. The 

 trunk begins to be raised at the same time that it inclines forwards and to 

 the side. The pubis is directed obliquely towards the side of the front leg. 

 B. Period of Single or Unilateral Contact. 1. At the beginning of this 

 period, that is when the posterior foot is about to quit the ground, and the 

 front foot is planted flat, the supporting leg continues to open or extend the 

 kuee-joinit, whilst the opposite one begins to be flexed. The bicotyloidean 

 axis is oblique, but from before backwards only, being otherwise horizontal ; 

 the trunk begins to rise at the same time that it inclines forwards and to the 

 side. The pubis is directed obliquely outwards, towards the side of the leg 

 in front. 2. In the middle of the period of unilateral support, that is when 

 the heel of the supporting leg quits the ground, it extends the articulation 

 of the knee to the utmost. In the leg that is suspended in the air, on the 

 contrary, the knee is flexed to its maximum amount. The bicotyloidean 

 axis is always oblique, but from above downwards only. It lies in a vertical 

 plane, and its lower extremity corresponds to the supporting limb ; the trunk 

 has reached its greatest elevation and at the same time its inclination for- 

 wards and to the side is at its maximum. The pubis is at its maximum of 

 obliquity as regards the path pursued on the side of the supporting leg. 

 3. At the close of the period of unilateral support, that is, when the sup- 

 porting leg touches the ground only by its metatarso-phalangeal portion, 

 and the free leg has passed the middle of its period of oscillation, the ankle- 

 joint of the supporting leg extends or opens whilst that of the knee remains 

 at its maximum of extension. The bicotyloidean axis becomes again oblique 

 from before backwards, and from above downwards ; but its obliquity is now 

 in the opposite direction, and the limb which was in front and above in the 

 period of double contact, is now behind and below. The trunk descends at 

 the same time that its forward and lateral inclination diminishes. The pubis 

 approximates the axis of the path. If the length of the steps increases, their 

 duration in general diminishes, whilst the falling of the trunk and its in- 

 clination always augment. The number of steps in a given time, or the 

 pace of walking, is partly dependent upon the length of the legs, and 



1 Carlet, Essais expe>imentals sur la Locomotion, in the Annales des Sci. Nat., 

 1872. The reader may also refer to Marty's Animal Mechanism, vol. xi, of the 

 International Scientific Series, and to Pettigrew's Animal Locomotion, vol. vii, of 

 the same scries. 



