are distributed through the internal parts of the bones. The 

 Endosteum (unlike the Periosteum) cannot be detached as a 

 continuous membrane. In most birds, however, the medullary 

 cavities of the long bones contain air. 



48. Long bones are the weight bearers, and are found in the 

 extremities or legs, and have a shaft and two ends. The compact or 

 hard structure, exists on the outside, being thickest at the middle and 

 inner side of the shaft, or wherever most weight falls, there covering 

 the cancellated or porous and light portions. The latter structure is 

 most abundant at the ends of the bone, so as to give a large, yet light 

 surface for joints, and it is there further covered by articular cartilage. 



49. Flat bones are found where important organs have to be 

 shielded. Thus, the bones of the head encase the brain ; the 

 shoulder-blade and ribs protect the heart and lungs, Hver, &c. ; while 

 the hip or pelvic bones cover the organs of generation. Flat bones 

 are made up of two layers of compact tissue, with a layer of 

 cancellated or porous tissue in the middle. 



50. Short and Irregular bones are found in the back-bone or 

 vertebral column, knee, hock, and lower portions of the limbs. These 

 bones are principally composed of cancellated tissue, covered with a 

 thin layer of the compact or hard structure, and are so arranged as to 

 bear weight, yet allow of movement, more particularly of a gliding 

 nature, and an " open and shut " motion. 



51. The Skeleton of the horse is said to be composed of about 253 

 bones (including the teeth), and is divided into Head, Trunk, and 

 Extremities. These divisions will, perhaps, be better understood by 

 the following tables. (See Plate V.) 



52. The Head is sub-Jivided into Cranium and Face. The former 

 consists of 20 separate bones, including 4 pairs, and 4 small bones in 

 in each ear ; while 61 bones are found in the face — nine pairs, three 

 single, and 40 teeth in the horse, and 36 in the mare. 



