14 A MANUAL OF ANATOMY 



It is triangular, and its direction is backwards and slightly down- 

 wards. Superiorly it presents an antero-posterior ridge for an 

 interspinous ligament, and inferiorly a grooved surface, also for 

 an interspinous ligament. It terminates behind in a bifid extremity, 

 which, in the case of the third, fourth, and fifth vertebrae, pre- 

 sents a distinct triangular notch. The bifurcated extremity gives 

 attachment to the deep fibres of the ligamentum nuchae. The 

 cervical spinous processes are very short, except those of the sixth 

 and seventh, especially the latter, and in this way backward flexion 

 or over- extension of the neck is not interfered with. 



The articular processes spring from the junction of the pedicle 

 and lamina at either side. Each is nearly circular, the plane being 

 oblique, and the surface almost flat. The superior pair look 

 backwards and upwards, and the inferior pair forwards and 

 downwards. 



The transverse processes {diapophyses) spring at either side from 

 the junction between the pedicle and lamina, and are serially 

 homologous with the transverse processes of a thoracic vertebra. 

 Each terminates in a projection, known as the posterior tubercle. 



The costal processes {pleurapophyses) project outwards from 

 either side of the body anteriorly, and are serially homologous with 

 the vertebral part of a rib. Each terminates in a projection, known 

 as the anterior tubercle, which, with the posterior tubercle of the 

 corresponding transverse process, gives attachment to the inter- 

 transversales muscles. 



The transverse and costal processes are connected, at a short 

 distance from the body, by a plate of bone, called the costo-trans- 

 verse lamella, which is deeply grooved superiorly for a spinal nerve, 

 this groove being continuous with the superior vertebral notch. 

 There is thus formed, at either side, an aperture, called the costo- 

 transverse foramen. This foramen is circular, vertical in direc- 

 tion (except in the case of the axis), and it transmits the following 

 structures : the vertebral artery ; the vertebral plexus of veins ; 

 and the vertebral sympathetic plexus of nerves. Though the 

 foramen is present in each transverse process, it does not give 

 passage to the foregoing structures in the case of the seventh. 

 The vertebral vein, however, may pass through it. In many cases 

 an additional foramen of small size is present on one or both sides, 

 lying behind the main foramen, and when this is so, it transmits a 

 small vein. The costo- transverse foramina of either side, when in 

 position, build up a canal, which is open in each intertransverse space. 



The neural foramen is situate;! behind the body, and is triangular, 

 with the angles rounded off. It is of larger size than in the thoracic 

 or lumbar vertebrae, its direction is vertical, and it lodges the sj^inal 

 cord with its membranes. 



The Atlas. — ^The atlas is the first cervical vertebra, and is so 

 named because it supports the head. Its distinctive characters are 

 the absence of a body and spinous process. It has the form of a 

 ring, narrow in front and wide behind, and its component parts 



