OSTEOLOGY. 25 



THE RIBS. 



The ribs are 36 in number, t8 on either side, forming the lat- 

 eral boundaries of the thorax, terminating below by cartilaginous 

 prolongations, the costal carti/ages. They articulate above with 

 the dorsal vetebrae. They are divided into stertial or true, eight 

 in number, and asternal ox false, the posterior ten. 



Genei'al Characteristics. — Each rib has an external convex 

 and internal concave smooth surface and an anterior or convex 

 border, a posterior border, showing a groove for the intercostal 

 vessels and nerves, a shaft and two extremities. 



The supei'ior extremity articulates with the vertebral column, 

 and shows a head with two demi-facets for the bodies of the ver- 

 tel)rae in front and behind, a neck below the head, and a tuberosity 

 for articulation with a dorsal transverse process. 



The infe?'ior extremity is excavated for the cartilage. 



The costal cartilages are flattened laterally, the first eight lying 

 on the sternum, the remainder articulating with the cartilage in 

 front. 



The len^tJi of the ribs increases from the first to the 9th, then 

 decreases ; their width from the ist to the 6th, then decreases. 



The 1st rib has no outer groove and no notch on its head. Its 

 cartilage is short and thick, and has an articular facet below for 

 the opposite. 



The i8th rib has no external channel, and the facet on its 

 tuberosity is confounded with that of its head. 



For thorax see Lungs. 



THE ANTERIOR EXTREMITY. 



This is divided into the shoulder, arm, forearm d.xv^ forefoot ox 

 hand. 



THE SHOULDER. 



In solipedes this consists of the scapula only, the clavicle being 

 absent. 



THE SCAPULA. 



The scapula or shoulder blade is a flat, triangular bone, lying at 

 the anterior and inferior part of the outer thoracic wall, articulat- 

 ing below with the head of the humerus. Its general direction is 

 downward and forward. 



It has two surfaces, extej-nal and internal, three angles, antei'ior 



