2 VETERINARY STUDIES 



Bones grow in diameter by the production of new bone cells at 

 the inner surface of the periosteum. They grow in length by the 

 development of bone cells in a cartilage matrix between centers 

 of bone formation in the shaft and extremities of the bone. A 

 long bone, for instance, may have three centers of ossification, 

 one in the shaft and one in each end, with a layer of this cartilage 

 matrix in the end between the centers of ossification. Bone cells 

 in the lacunas (spaces) throughout the substances of the bone, 

 prepare and deposit lime salts and other material. 



Fig. 2. — Horse's Skull. (Chauveau.) 



1, Premaxillary bone; 2, upper incisors; 3, upper canine teeth; 4, supe- 

 rior maxillary bone; 7, nasal bones; 8, lachrymal bone; 11, malar bone; 

 12, upper molar teeth; 13, frontal bone; 15, temporal bone; 16, parietal 

 bone; 17, occipital; 20, styloid processes; 24, parietal crest; 25, inferior 

 maxilla; 26, inferior molars; 28, inferior canine teeth; 29, inferior incisor 

 teeth. 



Structure and composition. — In a general way, bones consist 

 of surface plates of fine texture, hard bone with porous bone 

 inside of this. In the short, flat and irregular bones, this porous 

 bone makes up the whole interior. A long bone consists of two 

 enlarged extremities, composed of porous bone, and a shaft hav- 

 ing a surface of hard bone, covered on the inside with bone of the 

 porous texture. This porous bone then surrounds the medullary 

 canal which is characteristic of long bones. A thin layer of 

 cartilage covers all articular surfaces. The porous bone is filled 

 with red marrow and the medullary canal is filled with yellowish 

 marrow. 



Except at the articular surfaces, bones are covered by a thin 

 tough membrane, called periosteum. This is a matrix or mother 



