PRINCIPLES OF ANIMAL BIOLOGY 47 



Draw the limb, either wing or leg, omitting the body. Compare the 

 origin of the wings and legs of the chick with the origin of the hind legs 

 of the tadpole. 



B. DIVERGENCE OF ADULT VERTEBRATE LIMBS 



3. Hypothetical Pentadactyl (Five-toed or Five-fingered) Limbs. 

 Before comparing the adult limbs of the frog, pigeon, and man, study 



a chart representing the skeleton of a hypothetical pentadactyl limb. The 

 limbs of vertebrates have diverged in various ways from this typical form. 



3a. Fore Limb. Note the following parts: The shoulder girdle, com- 

 posed of clavicle, scapula, and coracoid, with perhaps a precoracoid; the 

 upper arm or humerus; the fore arm composed of radius and ulna; the 

 wrist with its ten carpal bones; the body of the hand with its five meia- 

 carpals; and the digits or fingers composed of phalanges. How many 

 phalanges in each? 



36. HindLimbs. Note the following parts: The pelvic girdle composed 

 of ilium, ischium, and pubis; the leg bone or femur; the lower leg with its 

 tibia and fibula; the tar sals, ten in number, in the ankle; the five meta- 

 tarsals forming the body of the foot; the digits or toes, composed of 

 phalanges. How many in each toe? 



4. The Limbs of Man. 



4a. The Arm. Compare the human arm bones with those of the 

 typical pentadactyl fore limb. Study the following structures: The pec- 

 toral or shoulder girdle, composed of the scapula or shoulder blade, the 

 clavicle extending from the shoulder to the sternum or breastbone, and 

 the coracoid, a hook-like process fused to the head of the scapula but 

 which in youth starts as a separate center of ossification; the arm bone 

 or humerus; the fore arm with its radius (on the thumb side) and the ulna; 

 the carpals in the wrist (number?); the metacarpals in the body of the 

 hand; and the phalanges. How many in each digit? 



46. The Leg. Compare the human leg bones with those of the typical 

 pentadactyl hind limb. Note similarities and differences. 



The pelvic girdle is fused into a single bone, the innominate, on each 

 side. The ilium is the broad expanded portion above the hip socket 

 or acetabulum. The ischium projects downward and somewhat backward 

 from the acetabulum. The two pubes of the opposite sides meet in the 

 middle line in front, from which point two branches project, one upward 

 and outward to the acetabulum, the other backward and downward to 

 the lower end of the ischium. 



In the leg proper observe: the femur or thigh bone; the tibia (larger) 

 and the fibula in the lower leg; the tar sals in the ankle (number?); the 

 metatarsals in the body of the foot; and the phalanges. How many in 

 each digit? 



