98 THE CHEST. 



toward the front and are by nature more freely movable 

 in women than in men. Most of the ribs have a head 

 divided by a little ridge into two facets for articulation 

 with the dorsal vertebrae, a flattened neck, a tuberosity at 

 the base of the neck with a facet for articulation with the 

 transverse process of the vertebra below, an angle, and 

 a shaft, which is externally convex and is grooved on its 

 lower edge for the intercostal vessels and nerve. The 

 first and second, eleventh and twelfth ribs, however, are 

 somewhat peculiar, the first two being shorter, flatter 

 and rather broader than the rest and the first having only 

 one facet on the head, while the last two have only one 

 facet on the head and no neck or tuberosity. 



The costal cartilages serve to prolong the ribs and 

 greatly increase the elasticity of the chest wall. They 

 grow longer down to the seventh and then decrease again 

 in length. 



The ribs, except the first and second, which are pro- 

 tected by the clavicle, are frequently broken. Such a 

 break causes pain in breathing and sometimes the end of 

 a rib pierces the lung tissue and swelling all over the 

 body results, due to the presence of air. Caries or death 

 of the rib is also frequent. Fracture of the sternum occurs 

 occasionally, generally from direct force, as from a blow 

 with the knee in foot-ball, and there may be dislocation 

 between the manubrium and gladiolus. 



Muscles of the Chest. The spaces between the ribs, 

 from the tubercle of the rib behind to the cartilage in 

 front, are filled by the external intercostal muscles, which 

 pass downward and forward from the lower border of 

 one rib to the upper border of the one below. There 

 are, therefore, eleven pairs of these muscles. There are 

 also eleven pairs of the internal intercostals , which com- 

 mence at the sternum and extend back to the angle of 

 the rib. These extend downward and backward. The 

 external intercostals raise and evert the ribs in inspira- 

 tion, the internal depress and invert them in expiration. 



The chief respiratory muscle, however, is the dia- 



