THE BONES OF THE TRUNK 



21 



tenth, eleventh, and twelfth (sometimes also the ninth) are peculiar, 

 and require separate descriptions. 



A Typical Thoracic Vertebra. — The body is larger than that of 

 a cervical vertebra, but smaller than that of a lumbar. When 

 viewed from above or below it is cordate or heart-shaped, being 

 broad ar.d hollowed out behind, and narrow ard rounded off in 

 front. The posterior depth of the body exceeds the anterior, 

 in adaptation to the backward curve of the vertebral column 

 in the thoracic region. The superior and inferior surfaces present 

 a raised rim round the circumference, due to the original epiphysial 

 plate, and this renders the whole of each surface slightly con- 

 cave from the periphery towards the centre. The anterior and 



Superior Articular Procos ^ 

 Superior Notch 



Superior Demi-facet '. 



Co^to-tiibercular Facet 



Inferior .\rticular Proce-is ' 



Fig. 13. — The Sixth Thoracic Vertebra (Lateral View). 



lateral surfaces merge gradually into each other, and are con- 

 cave from above downwards, the entire antero-lateral surface 

 being convex from side to side and pierced by numerous nutrient 

 foramina. Each lateral surface, close to the neural arch, presents 

 two articular demi-facets, superior and inferior, of which the 

 superior is the larger, and is situated upon the pedicular portion of 

 the body, the nferior smaller one being just in front of the lower 

 part of the inferior vertebral notch. These demi-facets are for 

 articulation with the heads of the ribs, and are called the costo- 

 capitular facets. When two vertebrae are in position the superior 

 demi-facet of the lower vertebra and the inferior demi-facet of the 

 upper form an articular cavity for the head of a rib. The posterior 

 surface of the body is concave from side to side, and presents 



