66 



Bones of the Spine. 



Tuberculum posterius 

 Arcus posterior 



x 



Massa lateral is 



Fovea dentis 



Sulcus arteriae 

 , vertebralis 



Fovea 



articularis 

 superior 



Processus 

 transversus 



Facies articularis posterior - 



Facies articularis superior 

 Groove for n. spinalis II 



Facies 

 ~ articularis 

 anterior 



_ Dens 



Foramen 

 transversarium 

 Massa lateralis 



' Arcus anterior 

 Tuberculum anterius 



Facies articularis inferior 



Processus transversus 



82. Atlas, 



from above. 



83. Epistropheus 



(0. T. axis), from the right. 



The atlas (see also Fig. 85) is especially characterized by the fact that it lacks the 

 main mass of the body. The only representative of a body is a narrow mass of bone in front, 

 arcus anterior, which presents, in the middle on its anterior surface, a small tuberculum 

 anterius, on its posterior surface a flat fouea dentis, covered with cartilage. The arch proper, 

 here called arcus posterior, is narrow, roundish and presents, in the middle behind, in place 

 of the processus spinosus, a small tuberculum posterius. Between the two arches lie the 

 massae later ales; each lateral mass possesses above an oval, concave articular surface, fovea 

 articularis superior, for articulation with the condylus occipitalis (oss. occipitalis) , below a 

 flat, rounded fades articularis inferior for articulation with the epistropheus. Lateral 

 from each massa lateralis the processus transversus projects far lateralward; it is devoid of 

 sulcus n. spinalis and of tubercles. Running out from the foramen transversarium is a groove 

 which leads behind the massa lateralis on the upper surface of the arcus posterior to the 

 foramen vertebrale, the sulcus arteriae vertebralis (for the a. and v. vertebralis ; n. suboccipi- 

 talis). Incisurae vertebrales are absent in the form in which they occur in the other cervical 

 vertebrae (vide infra). 



The epistropheus (0. T. axis) (see also Fig. 85) is especially characterized by a thick 

 cone, dens (tooth) (0. T. odontoid process), which ascends from the upper surface of the body ; 

 this presents, both in front and behind, a small, flat surface, covered with cartilage, fades 

 articularis anterior and posterior and ends above in a blunt tip. Near the toothshaped 

 process on the lateral part of the body lie the slightly convex fades articulares superiores, 

 directed obliquely lateralward and upward. The processus articulares inferiores and spinosus 

 show no especial deviations ; the processus transversi lack the tubercula anterius and posterius 

 as well as the sulcus n. spinalis ; the foramen transversarium is present below the facies ar- 

 ticularis superior as a short canal, curved laterally above. The incisura vertebralis inferior is 

 present and situated as in the other cervical vertebrae, i. e. in front of the processus articu- 

 laris. An exactly corresponding incisura vertebralis superior is however, absent; behind the 

 facies articularis superior, however, is a groove for the n. spinalis II. 



