THE SKELETON OF THE DOG. VERTEBRAE. 381 



is drawn out above into a very long compressed neural spine 

 (fig. 69, B, 4), which projects a long way forwards, and behind 

 becomes bifid and thickened, bearing a pair of flat downwardly 

 directed postzygapophyses. In the young animal the odontoid 

 process is readily seen to ossify from a centre anterior to that 

 forming the anterior epiphysis of the axis. 



The remaining five cervical vertebrae, the third to the 

 seventh inclusive, have rather flattened wide centra, obliquely 

 truncated at either end. The neural spine progressively increases 

 in size as the vertebrae are followed back. The transverse 

 processes vary considerably ; those of the third are divided 

 into a thicker backwardly-, and a more slender forwardly- 

 projecting portion ; those of the fourth and fifth mainly extend 

 downwards, and that of the sixth is divided into a horizontal 

 portion and a downwardly-projecting inferior lamella. All 

 the cervical vertebrae except the seventh have the bases of the 

 transverse processes perforated by the vertebrarterial canals. 

 The prezygapophyses in each case look upwards and slightly 

 inwards, while the postzygapophyses look downwards and 

 slightly outwards. 



THE THORACIC VERTEBRAE. 



The thoracic vertebrae are twelve or thirteen in number, 

 and all bear movably articulated ribs. As a group they are 

 characterised by their comparative shortness, and in the case 

 of the first eight or nine by the great length of the back- 

 wardly-sloping neural spine. The posterior thoracic vertebrae 

 approach in character the succeeding lumbar vertebrae. 



As type of the anterior thoracic vertebrae, take any one 

 between the second and sixth inclusive. The centrum is short, 

 and has its terminations vertically truncated. At the top of 

 the centrum, at both anterior and posterior ends on each side, 

 is a demi-facet (fig. 70, A, 4), which, together with that on the 

 adjacent vertebra, forms an articulating surface for the capitu- 

 lum of the rib. The neural arch is small and deeply notched 



