166 THE BONES. 



the pubis. The latter (Fig. 109, s") is thin and elongated, and follows the 

 direction of the inferior border of the ischium, with it circumscribing an oval 

 opening more or less spacious (Fig. 109, 22). Its inferior extremity extends 

 beyond the ischium, to curve inwards towards that of the opposite side, but 

 without uniting with it. We do not, therefore, find the pelvic symphysis in 

 Birds, and the pelvis is slightly open below, a circumstance which favours the 

 passage of the egg through the cavity and out of the cloaca. The cotyloid cavity 

 is perforated by an opening at the bottom, which passes through the bone. 



Thigh-bone. — The femur (Fig. 109, t) is articulated inferiorly with the 

 patella, tibia, and fibula. In all walking Birds, Uke the Gallinacae, it is long 

 and strong, as well as the bones below it. 



Leg-bones. — The patella (Fig. 109, u) is wide and thin. The tibia (Fig. 

 109, v) terminates, below, by two condyles separated by a groove, which becomes 

 articular behind. The fibida (Fig. 109, x) articulates by its head with the 

 external condyle of the femur, and is consolidated with the tibia ; it never 

 descends to the inferior extremity of that bone. 



Tarsal bones. — The tarsus appears to be altogether absent in Birds. Never- 

 theless, we may venture to consider, as a vestige of the bones of this region, a 

 small bony nucleus buried in a fibro-cartilaginous mass which gUdes on the 

 posterior pulley of the tibia. This nucleus (Fig. 109, y) represents the calcaneum 

 of Mammals. 



Metatarsal bone. — A single metatarsal bone is found in Birds, articulating 

 superiorly with the inferior extremity of the tibia, and terminating inferiorly by 

 three pulleys which support the three principal digits. This bone (Fig. 109, y) 

 shows in the Fowl, near its inferior third, a conical process turned backwards, 

 which serves as a base for the spur. Behind its superior extremity, it exhibits 

 another which may be considered as a consolidated metatarsal bone (Fig. 

 109, 23). 



Bones of the digital region (Fig. 109, z, etc.). — All the domesticated Birds have 

 four digits on the inferior members : three principal, directed forwards, and one 

 rudimentary, carried backwards. The first, designated as internal, median, and 

 external, articulate with the inferior pulleys of the metatarsal bones. The in- 

 ternal is formed by three phalanges, the second has four, and the third five. 

 These phalanges are formed something like those of the Carnivora ; the last is 

 pointed, conical, and enveloped in a horny sheath. The fourth digit, or thumb, 

 is composed of three pieces ; one of these, the first, is generally considered as a 

 rudimentary metatarsal bone. It is attached by fibro-cartilaginous tissue to the 

 inner and posterior aspect of the inferior extremity of the principal metatarsal 

 bone. 



