THE AXIS. 



121 



Fig. 150. 



Superior 

 articular 

 facet 



Articular facet on front 

 of odontoid process 



The axis from in front. 



Inferior articu- 

 lar facet 



part of it, may be fused with the skull around the foramen magnum. Such union 

 may be partial or complete, and is usually associated with an imperfect development 

 of the adas, especially on one side. There is reason to regard such cases as con- 

 genital. The transverse process and the paroccipital process of the occipital bone 

 may be connected by bone. 



The axis ' differs less from the other cervical verj^ebrae ; seen from below it pre- 

 sents no essential peculiarity. The body is very long even without the odontoid 

 process (the separated body of the atlas) which surmounts it. The odontoid^'- a 

 cylindrical process lower behind than 

 in front, ends above in a median ridge, 

 on either side of which is a rough, slant- 

 ing surface for the origin of the check 

 ligaments connecting it with the skull. 

 It bears an oval articular facet in front, 

 resting against one on the atlas, and a 

 smaller facet behind at a lower level 

 which forms part of a joint with the 

 transverse ligament. The lamincz^ in- 

 stead of being plates, are heavy and 

 prismatic, each with a rather sharp 

 upper edge, which, meeting its fellow, 

 forms a ridge on the spine. The spijioiis 

 process is heavy, projecting considerably 

 beyond the third. It varies greatly in- 

 length and in degree of bifurcation. 



The transverse process is small ; the anterior tubercle is a mere point or altogether 

 wanting. The transverse foramen is replaced by a short canal, so curved that its 

 upper opening looks almost outward. The superior artic2ilar surfaces are approxi- 

 mately circular facets on the upper surface of the body instead of on the arch, as 

 are all below ; they look upward and a little outward. Although nearly plane, they 

 present a very slight antero-posterior convexity. 



The seventh cervical vertebra, called vertebra proininens on account of its 

 long, knobbed spine, rather resembles the upper thoracics. The transverse foraryien 



is smaller than those above it, 

 Fig. 151. 2.nA\kie.a7iterior tubercle oixh^ 



transverse process is particu- 

 larly small and near the body. 

 The first thoracic ver- 

 tebra has the sides of the 

 upper surface somewhat raised 

 at the roots of the pedicles. 

 It has a complete facet for the 

 head of the first rib and a half- 

 facet at the lower border of the 

 body. Sometimes the former 

 is imperfect, being completed 

 on the intervertebral disk. 

 The facet on the transverse 

 process is smaller and less con- 

 cave than the ones followkig ; 

 sometimes it is even convex. 

 The ninth thoracic vertebra has no half- facet below. 



The tenth thoracic vertebra has a nearly complete facet above and none 

 below. 



The eleventh thoracic vertebra has a complete facet on the body and none on 

 the transverse process, which is small. 



The twelfth thoracic vertebra has a complete facet a little above the middle 

 of the body. The transverse process is broken up into the three tubercles. The 

 lower articular facets face outward. The spine is of the lumbar type. 



' Epistropheus. - Dens. 



Odontoid process- 



Articular facet for transverse ligament 



Anterior 

 articular 

 facet 



Spinous process 



Inferior articular 

 process and facet 



The axis from the side. 



Body 



Transverse foramen 



