60 HUMAN PHYSIOLOGY. 



continued as the ligamentum patellae, which is attached to the upper part of 

 the tibia. The action of this muscular group is to extend the leg, to flex 

 the thigh, and to raise the entire weight of the body, as in changing from the 

 sitting to the erect position. 



The biceps femoris muscle, situated on the outer and posterior aspect of the 

 thigh, arises from the tuber ischii, and is inserted into the head of the fibula. 



The semimembranosus and the semitendinosus muscles, situated on the 

 inner and posterior aspect of the thigh, are inserted into the head of the 

 tibia. Their combined action is to extend the hips and to flex the knee. 

 Acting from below, they assist in raising the body from the stooping position. 



The gastrocnemius muscle forms the enlargement known rs the calf of the 

 leg. It arises by two heads from the condyles of the fern ur. Its tendon, 

 the tendo Achillis, is inserted into the posterior surface of the heel bone. 

 Its action is to extend the foot and to raise the weight of the body in walking 

 and running. On the front of the leg are numerous muscles e. g., tibialis 

 anticus, peroneus longus, etc., the action of which is to flex the foot and to 

 antagonize the gastrocnemius. 



PHYSIOLOGY OF NERVE TISSUE. 



The nerve tissue, which unites and coordinates, the various organs and 

 tissues of the body and brings the individual into relationship with the ex- 

 ternal world, is arranged anatomically into two systems, termed the encephalo 

 or cerebro-spinal and the sympathetic. 



The encephalo or cerebro-spinal system consists of: 



1. The brain and spinal cord, contained within the cavities of the cranium 

 and the spinal column respectively, and 



2. The cranial and spinal nerves. 



The sympathetic system consists of: 



1. A double chain of ganglia situated on each side of the spinal column and 

 extending from the base of the skull to the tip of the coccyx. 



2. Various collections of ganglia situated in the head, face, thorax, abdomen, 

 and pelvis. All these ganglia are united by an elaborate system of inter- 

 communicating nerves, many of which are connected with the cerebro- 

 spinal system. 



HISTOLOGY OF NERVE TISSUE. 



The Neuron. The nerve tissue has been resolved by the investigations of 

 modern histologists into a single morphologic unit, to which the term neuron 

 has been applied. The entire nervous system has been shown to be but an 



