THE PIGEON 197 



The skeleton of the leg is made up of three divisions : a proxi- 

 mal, a middle, and a distal division. The proximal division is 

 composed of a single bone, the femur, which articulates in the 

 acetabulum. On the outer side of the head of the bone is a ridge, 

 the great trochanter. The patella, a small bone which is present 

 in the tendons passing over the knee, lies in front of the distal, or 

 lower, end of the femur ; it is usually lost when the leg is cleaned. 



The middle division is composed of two bones, the tibiotarsus 

 and the fibula. The first is a large bone which has been formed by 

 the fusion of the tibia with the proximal tarsal, or ankle, bones ; 

 the second is a slender bone, which is often fused with the first. 



The distal division is composed of the bones of the foot. They 

 fall into two groups: a vertical shaft, the tarso-metatarsus, and 

 the toes, or digits. The tarso-metatarsus is formed by the fusion 

 of the distal tarsal, or ankle, bones with the second, third, and 

 fourth metatarsal bones. The boundaries of the three metatarsals 

 are easily distinguished. No free tarsal bones are present, the 

 proximal row being fused with the tibia, as just stated, to form 

 the tibiotarsus ; the distal row with the metatarsals, to form the 

 tarso-metatarsus. 



Four digits are present. The first digit, which corresponds to 

 the big toe, projects backward and is raised above the ground. 

 It is composed of the first metatarsal bone, which is very small, 

 and two phalanges. The second digit is the innermost of the three 

 projecting forward; it has three phalanges. The third digit has 

 four phalanges, and the fourth digit has five. 



Exercise 39. Draw an outline of the bones of the leg and foot. 



The Axial Skeleton. This is composed of the skull and the 

 vertebral column, with the ribs and the sternum. The vertebral 

 column consists of a succession of vertebrae, which may be divided 

 into the following regions: the cervical, thoracic, lumbar, sacral, 

 and caudal. The boundaries separating these regions in birds 

 are not definite but are more or less arbitrary. The vertebrae of 

 all except the cervical region show a marked tendency to fuse 

 together ; the cervical region, on the other hand, is characterized 

 by great flexibility. 



