AVES. 241 



the ilium, beyond which it extends. The pubis is a slender rod 

 which, in the acetabulum, fuses with the ilium and ischimn. It 

 runs back below the latter, the obturator fissure separating the 

 two, and extends for some distance behind it. A wide space 

 separates the pubes and ischia of opposite sides. 



Free Limb (Fig. 69). The femur articulates with the acetabu- 

 lum by a preaxial head at right angles to the shaft, while its 

 proximal end is terminated by a facet which works against the 

 anti-trochanter, and on the postaxial side of which is a consider- 

 able elevation, the great trochanter. The distal end of the femur 

 is pulley-shaped. The main bone of the leg is the preaxial tibio- 

 tarsus with which the small rod -like postaxial fibula is partly 

 fused. The tibio-tarsus is a stout bone, much longer than the 

 femur, and with a pulley-shaped distal end. In front of the 

 knee-joint and fibula there is a small irregular bone, the patella. 



In the adult there is no separate tarsus, but in the embryo it 

 is represented by two cartilages, the proximal of which unites 

 with the preaxial tibia and forms the distal end of the tibio- 

 tarsus, while the distal fuses with the metatarsus. The ankle- 

 joint is thus between the two tarsal elements, and is said to be 

 mesotarsal i.e., in the middle of the tarsus. 



Four digits are present first, second, third, and fourth. The 

 metatarsals of the three last fuse with the distal part of the 

 tarsus to form the tarso-metatarsus. This is a rod of bone, the 

 distal end of which possesses three very distinct pulley-like sur- 

 faces for the three corresponding metatarsals. The small first 

 metatarsal is attached to the preaxial side of this end. The four 

 digits, of which the first is directed backwards, are completed 

 by 2, 3, 4, and 5 phalanges respectively. The terminal phalanges 

 support claws. 



4. The digestive organs (Fig. 70) consist of gut and appended 

 glands. The former is divided into mouth-cavity, gullet with 

 crop, proventriculus, gizzard, small intestine, and large intestine 

 opening into a cloaca. The glands are liver and pancreas. 



The mouth is bounded by the horny margins of the beak, 

 and, owing to the double joint by which the mandible is connected 

 with the skull, can be opened very widely. It leads into a large 

 mouth-cavity, upon the roof of which are two narrow slits, the 

 internal nares, largely overlapped by folds of mucous membrane. 

 Behind them is a small median Eustachian aperture, and posterior 

 2 16 



