48 LABORATORY DIRECTIONS IN 



5. The Limbs of a Frog. 



5a. The Fore Limb. Omit the pectoral girdle. Compare the bones 

 of the arm with those of the typical pentadactyl arm. Note the humerus 

 in the upper arm, and the radio-ulna in the fore arm. Which of the fused 

 bones is the radius? Study also the irregular carpal bones of the wrist 

 (number?); the metacarpals in the body of the hand, the one of the thumb 

 being rudimentary; the phalanges, present in the second, third, fourth, 

 and fifth digits, but wanting in the first. How many in each digit? 



56. The Hind Limb. Compare with the typical pentadactyl hind limb. 

 The pelvic girdle consists, on each side, of a long bone the ilium, extending 

 forward from the acetabulum; the ischium, a rounded flat bone behind 

 the acetabulum; and the pubis, a triangular bone below the acetabulum. 

 The latter is more or less translucent in fresh preparations. Each bone 

 forms part of the acetabulum. They may be readily distinguished in the 

 skeleton of a young frog. Observe the femur in the thigh, and the tibio- 

 fibula in the lower leg. Which edge of the latter represents the tibia? 

 There are four tar sals. Two of them are much elongated ; beyond these 

 are the other two, small irregular bones. Study also the metatarsals in 

 the body of the foot, and the phalanges in the toes. How many in each 

 toe? A rudimentary sixth toe may be present on the inner side of 

 the foot. 



6. The Limbs of a Pigeon. 



6a. The Fore Limb or Wing. Compare the bones of the pigeon wing 

 with those of the typical pentadactyl fore limb as well as with the 

 other forms already studied. 



The pectoral girdle consists of the scapula, a sword-shaped bone pro- 

 jecting back over the ribs; a coracoid, sloping downward and backward 

 and joining with the sternum or breastbone; and the two clavicles 

 fused to form thefurcula or wishbone. Observe the humerus in the upper 

 arm and the radius and ulna (larger) in the fore arm. Only two free 

 carpals are present and they may be hidden in the ligaments of the wrist. 

 See a thoroughly cleaned skeleton to find them. The remaining carpals 

 are fused with three rrietacarpals to form a large irregular bone, the carpo- 

 metacarpus, consisting of two rods joined at the ends. The larger of the 

 two rods represents the second metacarpal. At its base, on the anterior 

 edge, is a tubercle which represents the first metacarpal. The third 

 metacarpal is represented by the more slender one of the two rods. 



Only three digits are represented by phalanges. The first finger has 

 a single spine-like or triangular phalanx. The second has two phalanges; 

 and the third finger one, which may be closely applied to the first phalanx 

 of the second finger. 



66. The Hind Limb. Compare the leg of the pigeon with the typical 

 pentadactyl limb and with those of the other forms studied. ' 



