10 



VERTEBRAL COLUMN. 



are pierced by numerous small foramina for the passage of blood-ves- 

 sels, one or two of which foramina situated near the middle of the pos- 

 terior surface are much larger than the others. 



The arch consists of two symmetrical portions -which spring, one on 

 each side, fi'om the ])Osterior surface of the l)ody, and meet in the 

 middle line behind. The anterior part of each half, rounded and nar- 

 row, is called the pedicle ; the posterior part is broad and flat, and is 

 called the lamina (ncurapophysis, Owen). Tlie concavities on the 

 upper and lower borders of the pedicles are named notcJtes, and consti- 

 tute by the apposition of those of contiguous vertebra?, the ■inierrertehral 

 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, Ow.) projects backwards from the 

 arch in the middle line. The transverse 2>roccsses (diapophyses, Ow.), 

 placed one on each side, project outwards from the anterior part of the 

 arch. The articular processes (zygapophyses, Ow.), two superior and 

 two inferior, project upvrards and downwards from a point near the 

 junction of pedicle and lamina. Tlicir articular surfaces, coated with 

 cartilage, in the superior pair look backwards, and in the inferior for- 

 wards, so that the former face the latter in adjoining vertebra}. 



lihe forame/i is bounded anteriorly by the body, posteriorly and later- 

 ally by the arch. The series of rinr/s thus formed, united by ligaments, 

 constitutes the neural canal, in which the spinal cord is contained. 



Texture. — The bodies of the vertebra? are almost entirely composed 

 of spongy substance, the surface being covered with only a thin layer 

 of compact tissue. Venous canals, commencing at the larger foramina 

 behind, traverse the cancellated structure. The arch and processes 

 contain a much smaller proportion of spongy substance, being covered 

 Avith compact tissue of considerable density in some places. 



GROUPS OF VERTEBRA. 



The vertebra? are divided into five groups, named from the* regions 

 which they occupy, cervical, dorsal, hmibar, sacral, and cocci/c/cal. 



Cervical Vertebrse. — These are seven in number. The first and 

 second are so peculiar in form, as to require a separate description. 

 The following characters belong to the five lower vertebrae. 



Fig- •'•• Fig. 5.— Thikd Cervical Vertebka. (A. T.) i 



A, from above and slightly from behind ; T>, from 

 the side. 1, the body ; belaud a, the pedicle and 

 inter-vertebral notch ; 3, lamina ; 4, vertebral ring, of 

 a triangular form ; 5, bifid spinous i>rocess ; 6, 6*, 

 transverse jirocess — 6, posterior, 6*, anterior tubercle ; 

 a, foramen in tlie transverse process transmitting the 

 vertebral artery ; 7, 7', articular processes — 7, tlie 

 superior, 7', the inferior. 



The hod// is small and l)roader from side 

 to side than from before backwards. Its 

 superior surface is transversely concave from 

 the upward projection of its lateral margins, 

 and is sloped down anteriorly. Tlie under 

 ^ surface on the contrary is rounded off at the 



sides, while its anterior margin forms a marked projection downwards. 



