400 MUSCLES WHICH KEEP THE BODY ERECT. 



may be observed, that the connexion of the bodies of the 

 vertebrae, by the intervertebral cartilaginous matter, and of the 

 plates behind, by the elastic ligament, renders these articulations 

 perfectly anomalous ; and very different in their principles from 

 the articulations in general. 



In no part of the skeleton is this tendency to bend forward 

 more strongly perceived thac in the head. When we are 

 awake, and the muscles in a healthy situation, it is effectually 

 restrained, and the head kept erect, by the splenius and corn- 

 plexus, and other muscles, which act from the spine below, 

 upon the back part of the head and the vertebrae of the neck. 



When we stand on one foot, some very different muscles are 

 called into action ; the tendency of the body is to fall sideways, 

 towards the foot which is raised from the ground. To coun- 

 teract this tendency the two larger peronei muscles, which are 

 situated on the outside of the leg, act from the foot, to keep the 

 leg erect. The vastus externus acts upon the same principle 

 from the leg upon the os femoris. The gluteus medius and 

 minimus, and the muscle of the fascia, act from the os femoris 

 upon the pelvis and trunk ; while the quadratus lumborum, 

 and those abdominal muscles which draw the spine to that side, 

 continue the operation : and so do likewise the muscles which 

 act on the same side of the neck and head. 



In rising from a seat, the tibialis anticus acts very powerfully, 

 to keep the tibia erect, and prevent it from inclining backwards. 

 The two vasti, and the cruraeus, raise up the os femoris, while 

 the gluteus maximus, the sernitendinosus, and semimembra- 

 nosus, and the long head of the biceps, extend the trunk of the 

 body. 



There are several modes of walking, which are different from 

 each other, in a small degree. 



We may walk, for example, with the knee of the hind limb 

 straight or bent, as we bring it forward. This circumstance is 

 merely a matter of accommodation. But there are two essential 

 processes in walking, viz. 1. Projecting one foot forward, and 

 placing it on the ground while thus projected : and 2. Moving 

 the body over that foot. 



