64 THE FROG chap. 



muscles, acting either singly or in concert. The contractions 

 of these muscles are brought about by nervous impulses sent 

 from the brain or spinal cord along nerves which branch 

 out and are distributed to the muscles, thus bringing the 

 whole of the complex machinery which affects the movements 

 of the animal under the direct control of its will. 



PRACTICAL DIRECTIONS. 

 The Joints and Ligaments. 



1. The hip-joint. Strip off most of the muscles from the thigh and 

 the adjacent parts of the pelvis ; decalcify in weak acid and then wash 

 thoroughly. Cut the femur through lengthwise and continue the section 

 through the pelvic girdle (Fig. 15). 



Note : a. The cartilage of the acetabulum and head of the femur ; 

 the pcrichondriuui and periostcuju. {h) The capsular ligament and its 

 relations to the synovial capsule. Observe that the hip-joint is a cup 

 and da II joint. Sketch. 



In a prepared wet skeleton — 



2. Examme and compare a hinge-joifit {e.g., elbow or knee). 



3. Examine the cartilaginous union between the bones of the shoulder- 

 or hip-girdle (iinmo-rcalilc or imperfect joints). 



4. Examine the joints and ligaments of the vertebral column. 



The Muscles. 



1. Remove the skin from part of the body and legs of ^ preserved 

 frog (the one you have already dissected ns ill do). Then clear away the 

 fascia here and there and separate sonne of the muscles 1)V dissecting 

 away the connerti\-e tissue which binds them together. Notice the 

 different forms of the muscles in different parts. (Compare Fig. 16 

 and p. 63). 



2. In the hind-leg carefully divsect away the connective tissue 

 investing the gastrocnemius muscle (Figs. 16 and 17), and trace it 

 upwards towards the thigh, and downw.irds towards the foot, cutting 

 :nvay an}- of tile otlier muscles which obscure the view. Notice the 

 tictly^ and llie tendons of origin ntid insc} tion (p. 60). Sketch. 



liend the fool upon the shank as in the .ndinary sitting position of the 

 frog. Hold the thigh firmly with one hand, and with the other take hold 



