THE FROG. 189 



in the fore leg, named from the body outward, arm, fore- 

 arm, and hand (for this limb is homologous with the 

 upper limb or arm of man) ; and in the hind leg, thigh 

 (QY femur), shank, and foo t. 



Make drawings of both hand and foot as seen from 

 above. Compare the two as to the number of digits or 

 phalanges in each, and the number of joints in each digit. 

 In the males the base of the inner digit of each hand is 

 greatly swollen in appearance. Such a peculiarity of sex, 

 occurring entirely apart from the sexual organs, is called 

 a secondary sexual character. 



Study of Superficial Leg Muscles. Cut the skin around 

 the base of one of the hind legs, dissect it free from the 

 underlying muscles half the length of the thigh, and then 

 strip it off over the foot like a stocking, wrong side out. 

 Now study the arrangement of parts in this extremity. 

 The whitish muscles now cover all other parts. Dissect 

 apart, without freeing at their ends, several of the large 

 muscles on the back of the femur, and find nerves and 

 blood vessels and bone. Free at its edges the large muscle 

 (gastrocnemius) of the back of the shank, and observe : 



1. The connective tissue enveloping all the muscles, 

 and binding them together. 



2. The connective tissue sheath enveloping each indi- 

 vidual muscle. 



3. The white, strong tendon, in which this muscle 

 terminates at its outer end. Follow this tendon (tendo 

 AcMllis) outward, along the sole of the foot, and see it 

 dividing, and its divisions coalescing with the tendons of 

 other shorter muscles of the foot, and extending to the 

 toes. Pull this tendon toward the body, and observe the 

 effect on the foot. 



4. The close attachment of the inner end of this muscle 

 at the back of the knee joint. 



