DEVELOPMENT OF GALLUS 



223 



surrounding membranes. At an early stage it turns and lies on 

 its left side, and later, its body lies along the long axis of the egg 

 with its head near the blunt end of the shell, which is where 

 the air-chamber is situated. Its beak pierces the inner shell- 



V 0---P 



o-t. 



3 w 



Fig. 106. — Gallus : views of the (cartilaginous) skeleton of the limbs and 

 girdles of embryo chicks, A and B, after 5 days' C and D after 9 days' 

 incubation, as seen from the left side. 



A and C, pectoral girdle and limb ; B and D, pelvic girdle and limb. 

 Note that in the earlier stage the pubis points forwards, c, coracoid ; ca, 

 carpals ; dt, distal tarsals (which will fuse with the metatarsals to form the 

 tarso-metatarsus) ; fe, femur ; fi, fibula ; h t humerus ; i, ilium ; is, ischium ; 

 mc, metacarpal ; mt, metatarsal ; p, phalanx ; pt, proximal tarsals (which 

 will fuse with the tibia to form the tibio-tarsus) ; pu, pubis ; r, radius ; s, 

 scapula ; t, tibia ; u, ulna. 



membrane, and it begins to breathe the air in the air-chamber 

 into its lungs, often making the characteristic " peep peep " 

 sound. The connexions between the pulmonary arteries and 

 the dorsal aorta (ductus arteriosus) disappear, and more 

 and more blood passes through the lungs. The yolk-sac has 



