42 



OSTEOLOGY. 



notches are deeper, but narrower, than the inferior. The laminse are narrow, 

 long, thinner above than below, and overlap each other; inclosing the spinal 

 foramen, which is very large, and of a triangular form. The spinous processes 

 are short, bifid at the extremity, to afford greater extent of surface for the attach- 

 ment of muscles, the two divisions being often of unequal size. They increase 

 in length from the fourth to the seventh. The transverse processes are short, 

 directed downwards, outwards, and forwards, are bifid at their extremity, and 

 marked by a groove along their upper surface, which runs downwards and out- 

 wards from the superior intervertebral notch, and serves for the transmission of 

 one of the cervical nerves. The transverse processes are pierced at their base by 

 a foramen, for the transmission of the vertebral artery, vein, and plexus of nerves. 

 Each process is formed by two roots ; the anterior root arises from the side of the 

 body, and corresponds to the ribs ; the posterior root springs from the junction of 

 the pedicle with the lamina, and corresponds with the transverse processes in the 

 dorsal region. It is by the junction of these two processes, that the vertebral 

 foramen is formed. The extremities of each of these roots form the anterior and 

 posterior tubercles of the transverse processes. The articular processes are oblique: 

 the superior are of an oval form, flattened, and directed upwards and backwards; 

 the inferior downwards and forwards. 



The peculiar vertebrae in the cervical region are the first or Atlas; the second or 

 Axis; and the seventh or Yertebra prominens. The great modifications in the form 

 of the atlas and axis are- to admit of the nodding and rotatory movements of the 

 head. 



The Atlas (fig. 2) is so named from supporting the globe of the head. The chief 



Fig. 2. 1st Cervical Vertebra or Atlas. 



Trans. Procc 



foramen for 

 Vertebral Ar/f. 



Grooire fcr Verz/eA. Art ? 

 and J.'-' Cerv,Ne<rva 



peculiarities of this bone are, that it has neither body nor spinous process. The 

 body is detached from the rest of the bone, and forms the odontoid process of 

 the second vertebra, the parts corresponding to the pedicles pass in front and 

 join to form the anterior arch. The atlas -consists of an anterior arch, a posterior 

 arch, and two lateral masses. The anterior arch forms about one-fifth of the 

 bone ; its anterior surface is convex, and presents about its centre a tubercle, for 

 the attachment of the Longus colli muscle ; posteriorly it is concave, and marked 

 by a smooth oval or circular facet, for articulation with the odontoid process of 

 the axis. The posterior arch forms about two-fifths of the circumference of the 

 bone ; it terminates behind in a tubercle, which is the rudiment of a spinous 

 process, and gives origin to the Eectus capitis posticus minor. The diminutive 

 size of this process prevents any interference in the movements between it and 

 the cranium. The posterior part of the arch presents above a rounded edge ; 

 whilst in front, immediately behind each superior articular process, is a groove, 

 sometimes converted into a foramen by a delicate bony spiculum which arches 



