OSTEOLOGY 9 



The sternum. — This is located in the front and lower portion 

 of the chest, and extends from before to behind. It consists of 

 six or seven pieces of cartilaginous bone and has distinct pro- 

 longations of cartilage from both the front and rear ends. On 

 each side are articular surfaces for the first eight ribs. The 

 sternum is commonly called the breast bone. 



Ribs. — These usually number 18 pairs, and are described as 

 the first, second, third, etc., beginning with the front pair. 

 They all articulate above with the dorsal vertebrae; the lower 

 ends of the first eight articulate with the sternum by means of 

 cartilages. The remaining ten connect with the sternum by 

 means of long cartilages, each of which rests against the pre- 

 ceding one. The ninth, or first asternal, rib is united rather 

 closely to the eighth, which articulates with the sternum. 



The shaft shows external convex and internal concave sur- 

 faces and two borders : anterior or front, and posterior or rear. 

 The superior or upper extremity shows a head and a small pro- 

 jection, the tuberosity. These articulate with the dorsal ver- 

 tebra? as already explained. Function of the ribs is to form a 

 supporting and movable wall for the chest, protecting the soft 

 organs and performing a very important function in opening 

 the chest for respiration. 



Practical application. — The student should now study, for 

 himself, the part played by each group of vertebra? in determin- 

 ing the conformation of its region. Take, e.g. the cervical, dor- 

 sal, lumbar, and sacral groups, and note what relation they bear 

 to length of neck, height and shape of withers and length of 

 back, width and length of loin, length and slope of the croup. 

 The student should also study the influence of shape of rib 

 upon width of back and shape of sides. Record fully by notes 

 and drawings. 



Common disorders. — Domestic animals are subject to many 

 disorders of this region but few of these affect the vertebra? 

 especially. There are occasional fractures and dislocations. 

 Tuberculosis, osteoporosis, etc., may affect these bones as well 

 as others. Sometimes adjacent vertebra? unite by a bone-form- 

 ing process following inflammation (ostitis) most frequently 

 resulting from injury. 



