28 Anatomy of Skeleton 



Thus the tenth rib frequently articulates with one vertebra only, the tenth dorsal, 

 so that the ninth dorsal vertebra may only present on its body a large " demi-facet " 

 above, and none below : usually, however, there is at least an indication of the former 

 presence of the lower rib, if not an actual articular surface, and there is always a 

 facet on the transverse process. 



The TENTH VERTEBRA has a whole facet, or nearly a whole facet, on its body 

 above, and none below, with one on the transverse process : this last, however, may 

 not show a recognisable articular surface. 



The ELEVENTH AND TWELFTH DORSAL VERTEBRAE are alike in having 

 complete single facets on each side of the bodies with none on the transverse 

 processes, which are reduced to thick, stunted, and tuberculated projections. The 

 spines are also reduced to short and somewhat pointed projections extending 

 nearly horizontally backwards. 



Though alike in these characters, the two vertebrae may usually be distinguished 

 by their articular processes, for whereas those of the eleventh are dorsal in character, 

 those of the twelfth are only dorsal above, the lower ones being turned out like those 

 in the lumbar series : it must be added, however, that occasionally, though rarely, 

 this double character is present in the eleventh segment, in which case both upper and 

 lower processes in the twelfth vertebra exhibit the lumbar type of conformation. 



In these last two dorsal vertebrae the spinal foramen widens owing to the presence 

 of the lumbar enlargement of the cord. 



The centrum of a typical dorsal vertebra is covered in front and laterally by the 

 fibres of the wide anterior common ligament which separates it from the intercostal 

 arteries that pass out on it to their destinations, and from the other structures that are 

 described as being in relation with the column in the posterior mediastinum. But 

 one of these, the Aorta, usually leaves its impress on the middle vertebrae notwith- 

 standing, in the shape of a raising of the concave side aspect of the body, so that it 

 presents a flat surface for the support of the artery through the ligament. This 

 flattening of the left side may affect the upper and lower margins as well, giving an 

 asymmetrical appearance to the bone examined, and is accompanied by a difference 

 in the aspect of the texture of the bone as seen on the surface. The " aortic impression " 

 produced in this way is best marked on the fifth body, but can be followed down from 

 this for the succeeding two or three vertebrae, finally fading towards the front of the 

 bones at about the ninth segment ; in some columns the impression cannot be demon- 

 strated certainly. Large vascular -foramina can be seen, mainly on the sides of the 

 bodies, which transmit veins through the ligament, or round its edges, to the azygos 

 veins : in the bodies of the vertebrae these lateral channels are connected with the 

 posterior one, which makes its exit by means of one or two foramina on the neural 

 surface of the body, through which veins pass beside the posterior common ligament 

 to join the spinal venous plexus (anterior longitudinal spinal veins), which extends 

 behind the vertebral bodies for the length of the column. 



Indications of the diverging nature of the fibres of the stellate ligaments of the 

 rib-heads can be seen in the markings that lie round the facets, and the attachment of 

 the anterior common ligament to the upper and lower parts of the bodies can usually 

 be recognised by the markings on the bones. 



The dorsal bodies vary in their shape and in the relations between their measure- 

 ments. This can be illustrated by the outlines of the upper surfaces of the bodies 

 taken from a normal column (Fig. 24). Comparing the sagittal measurement with the 

 transverse between the margins of the upper facets, the first body gives 9 : 18, the 



