AYES. 239 



is produced downwards into a prominent vertical plate, the keel, 

 which is deepest in front. 



(2) Appendicular Endoskeleton. The long bones possess epi- 

 physes, as in the frog. Girdle and free limb can be distinguished 

 in both fore- and hind-limbs. 



(a) Fore-Limb Shoulder-girdle (Fig. 69). The scapula is a 

 backwardly-directed, blade-like bone, united closely in front with 

 a rod-like coracoid, the other end of which articulates with the 

 sternum. These two bones make with one another an acute 

 angle, open behind, and the glenoid cavity is situated at their 

 point of union. In front of this the slender clavicle is attached, 

 which curves backwards and downwards, and unites with its 

 fellow in the middle line to form the furcula ("merry-thought"). 



The union is effected (?) through the intermediation of a small inter- 

 clavicle, which forms in the Fowl a small, laterally flattened disc. 



Free Limb (Fig. 69). The humerus possesses a proximal head 

 for articulation with the glenoid, and a distal, pulley-like trochlea, 

 which presents preaxial and postaxial articular surfaces for the 

 radius and ulna. Two distinct bones, radius and ulna, support 

 the antebrachium. The preaxial radius is straight and slender, 

 the postaxial ulna relatively stout. The proximal end is pro- 

 duced into an olecranon process. 



The carpus is made up of two small bones, the radiale and 

 ulnare, which articulate with the radius and ulna respectively. 

 First, second, and third metacarpals are present, closely united 

 proximally. The first is small, and projects but little beyond 

 the fused part. The second is long and stout, and the third long 

 and slender. The three digits are completed by phalanges, the 

 first and third possessing a single small one, while two large 

 phalanges terminate the second digit. 



(1)) Hind-Limb Hip Girdle (Fig. 68). Each half, or os 

 intwminatum, is separate from the other, and made up of three 

 elements, ilium, ischium, and pubis, all three of which contribute 

 to the formation of the acetabulum, a rounded cup, not floored by 

 bone, on the outer side of the girdle. The large ilium extends 

 forwards and backwards above the acetabulum. It meets and 

 fuses with the anterior ends of the ischium and pubis to bound 

 the acetabular cavity, above which it presents a smooth surface, 

 .the anti-trochanter. The " sacrum " is closely connected with the 



