32 Anatomy of Skeleton 



distinguished with any certainty on the bones. The Longissimus Dorsi is inserted into 

 the processes. 



These post-vertebral muscles also make markings on the sides of the spines, but 

 separate indications are not to be found : possibly the more tuberous state of the spinal 

 surface in the upper three or four dorsal vertebrae is associated with the insertion here 

 of Semispinalis dorsi. 



Notice how the laminae and spines overlap the succeeding bones and cover in the 

 canal : such an arrangement makes it probable that the ligamenta subflava have their 

 upper attachments higher up on the neural surface of the broad laminae than is the 

 case in the cervical region, and inspection of this surface shows that it is so, the upper 

 line made by the ligament crossing at the mid-level of the lower articular surfaces 

 and indicating that the ligament becomes continuous externally with the capsule of 

 the joint. The presence of strong ligamenta subflava in this region shows that these 

 are not primarily concerned in covering the canal : they are to resist flexion forwards 

 of the column, and we therefore find that they increase in strength from above down- 

 wards, reaching their maximum in the lumbar region. The line on the neural surface 

 of the laminae enables us to divide this surface into an upper, separated from the dura 

 mater by vascular fatty tissue, and a lower for the attachment of the interlaminar 

 ligaments and fibrous tissue continuous with that of the interspinous ligaments. 



The obliquity of the spinous processes varies in the different parts of the series, 

 being greatest in the middle, where the spine of the seventh dorsal vertebra is usually 

 the longest and most obliquely directed. With the exception of the upper three or 

 four, the spines of the series are somewhat tapering and thin, but enlarging at their 

 extremities to form tubercles : these are covered by supra-spinous ligaments and give 

 origin to Trapezius, Rhomboids, and Latissimus dorsi muscles, according to their 

 position. 



Below the seventh, the obliquity of the spines decreases, being practically not 

 apparent in the last two vertebrae of the region. Individual spines frequently deviate 

 to one side or the other, without any change in the central position of the bodies. 



It is clear that, as a result of their directions, the levels of the tips of the spines as felt on the 

 surface of the body do not correspond with those of the bodies to which they belong, and it is 

 important when considering levels or surface markings of internal structures to bear clearly in 

 mind this distinction between bodies and spines. Each spine differs from the others in its relation 

 to the levels of lower bodies, but a rough rule may be remembered for practical purposes, that in 

 the middle vertebrae, fourth to ninth, the tip of a spine is about opposite the disc between the two 

 bodies next below its own body; the other levels can be obtained without much trouble on an 

 articulated column. 



The rounded shape of the spinal foramen is first reached in the fourth segment : 

 it persists throughout the series until the lumbar enlargement of the cord, which 

 commences just above the level of the eleventh dorsal vertebra, widens out the canal 

 laterally in that bone and in the twelfth, so that the foramen in this last is the widest 

 and largest in the whole series. 



LUMBAR VERTEBRA. 



Distinguished by their large size and massive structure, with absence of transverse 

 foramen and costal facets. They present large kidney-shaped bodies, slightly deeper 

 in front than behind : pedicles thick, with very shallow upper notches : transverse 

 processes comparatively slender, with the small accessory tubercles behind them. 

 Articular processes vertical and curved transversely so that the lower pair look 



