THE VERTEBRAL COLUMN. 



SPINOUS PROCESS 



TRANSVERSE 

 PROCESS 



SUP. ARTIC. PROCESS 



I. THE VERTEBRAL COLUMN. 



The vertebral column is composed of a series of bones called vertebrae, which are 

 united together, for the most part, by joints and elastic substance in such a manner 

 that, although the amount of motion allowed between each pair is slight, the 

 aggregate is sufficient to give the column very considerable flexibility. The vertebra 

 are originally thirty-three in number. Of these, the upper twenty-four remain 

 separate in the adult, retaining their mobility, and are hence called moveaUe or true 

 vertebrae. They are succeeded by five others, which rapidly diminish in size from 

 above downwards, and which are united into one mass called the sacrum ; beyond 

 the sacrum are four dwindled terminal members of the series, which as age 

 advances, likewise become more or less united, and form the coccyx. These sacral 

 and coccygeul vertebrae are known as thefaed we false vertebrae. 



General characters of the vertebrae. The general characters are best seen 

 in the vertebrae placed near the 

 middle of the column, of which 

 the tenth dorsal vetebra, shown 

 in fig. 1, may serve as an example. 

 Each has more or less the form of 

 a ring, and presents for considera- 

 tion a body, arch, processes, and 

 the enclosed spinal foramen. 



The body or centrum is a short 

 cylinder or disc, which forms the 

 anterior part of the vertebra. Its 

 superior and inferior surfaces are 

 flattened and connected to the 

 next vertebrae by strong and elas- 

 tic intervertebral discs. On the 

 front and sides it is convex hori- 

 zontally, but slightly concave 

 from above downwards ; its pos- 

 terior surface forms part of the 

 ring, and is slightly concave from 



Side to Side. J.hese vertical pjg_ j TENTH DORSAL VERTEBRA, FROM ABOVE. (Drawn 

 surfaces are pierced by numerous by D- Gnn.) 



small foramina for the passage 



of blood-vessels, and near the middle of the posterior surface are one or two much 

 larger than the others. 



The arch (neural) consists of two symmetrical portions which spring, one on each 

 side, from the posterior surface of the body, and meet in the median plane behind. 

 The anterior part of each half, thick and narrow, is called the pedicle ; the posterior 

 part is broad and flat, and is called the lamina. The concavities on the upper and 

 lower borders of the pedicles are named vertebral notches (fig. 2, B), and consti- 

 tute, by the apposition of those of contiguous vertebrae, the intervertebral foramina, 

 a series of rounded apertures, which communicate with the vertebral canal, and 

 transmit the spinal nerves and blood-vessels. 



The spinous process (neural spine) projects backwards from the arch in the 

 median plane. The transverse processes, placed one on each side, project outwards 

 from the arch at the junction of the pedicle with the lamina. The articular pro- 

 cesses (zygapophyses), two superior and two inferior, project upwards and downwards 

 opposite the attachment of the transverse processes ; their articular surfaces, coated 



