70 



MAMMALIAN ANATOMY 



the. second rib. Each succeeding vertebra has two half-facets, one 

 at each end, until the eleventh is reached, where the articulation for 

 the rib is more caudal ; wherefore the eleventh, twelfth, and thirteenth 

 vertebra? have each a single entire facet. 



With the exception of the first, the eleventh, the twelfth, and the 

 thirteenth rib, every rib is cephalic to its own vertebra ; for example, 

 the seventh rib is attached between the sixth and seventh vertebra?. 

 Another character common to all the thoracic vertebra? (except the 

 last three) and useful for rapid identification is found in the smooth 

 articular facet on the ventral surface of the transverse process. This 

 facet joins the tubercle of the rib. 



The cephalic thoracic vertebra? have the general form of the last 

 cervicals ; the caudal thoracic closely resemble the cephalic lumbars. 

 A typical thoracic vertebra should be therefore selected from the 

 middle of the region. 



A TYPICAL THORACIC VERTEBRA. 



The Sixth Thoracic Vertebra. The body has equal cephalo- 

 caudal and transverse diameters, but it is somewhat flattened from the 

 dorsal to the ventral side. The dorsal surface is quadrate and flat. 



Fid. 45. 



Transverse Process. 



Articular facet on 

 under Surface of Trans- 

 verse Process for Tuber- 

 cle of Bib. 



Cephalic Articular Surface. 



A THORACIC VERTEBRA, VENTRAL ASPECT. 



The ventral surface (Fig. 45) is convex from side to side and 

 decidedly concave from the cephalic toward the caudal end. 



The outline of the cephalic surface (Fig. 4(3) is approximately a 

 circle, a small arc only being cut from the dorsal side. The margin 

 is sharp and well defined dorsally and ventrally, but at each lateral 

 dorsal angle it is rounded and presents the rather obscure cephalic 

 half-facet for part of the head of the sixth rib. The caudal surface 

 (Fig. 47) is triangular ; each dorsal lateral angle is prolonged into a 

 small process. This process exhibits on its caudal surface the half- 



