68 SPECIAL ANATOMY OF THE SKELETON 



especially if the muscles in the loins are well developed and the process incurved. The} 7 are much 

 larger and farther apart than in the thoracic region. In the sacral region the furrow is shallower, 

 presenting a flattened area which terminates below at the most prominent part of the posterior 

 surface of the sacrum, formed by the spinous processes of the third sacral vertebra. At the bottom 

 of the furrow may be felt the irregular posterior surface of the bone. Below this, in the deep 

 groove leading to the anus, the coccyx may be felt. The only other portions of the vertebral 

 column which can be felt from the surface are the transverse processes of three of the cervical 

 vertebrae, viz., the first, the sixth, and the seventh. The transverse process of the atlas can be 

 felt as a rounded nodule of bone just below and in front of the apex of the mastoid process, 

 along the anterior border of the Sternomastoid. The transverse process of the sixth cervical 

 vertebra is of surgical importance. If deep pressure be made in the neck in the course of the 

 carotid artery, opposite the cricoid cartilage, the prominent anterior tubercle of the transverse 

 process of the sixth cervical vertebra can be felt. This has been named Chassaignac's tubercle, 

 and against it the carotid artery may be most conveniently compressed by the finger. The 

 transverse process of the seventh cervical vertebra can also often be felt. Occasionally the ante- 

 rior root, or costal process, is large and separate, forming a cervical rib. 



Applied Anatomy. It is frequently necessary to locate certain vertebrae. Several of them 

 can be easily found and identified. The seventh cervical spine is conspicuously prominent; and 

 when the skin over it has been marked with a blue pencil the spine of the sixth cervical above and 

 of the first thoracic below may be located. The spine of the third thoracic vertebra is on a level 

 with the root of the spine of the scapula. The spine of the fourth lumbar vertebra is on a level 

 with the highest point of the iliac crest. When one or two vertebrae have been definitely recog- 

 nized the other ones can be found by counting the spines from a fixed pointer from fixed points. 

 Over the fifth lumbar spine there is no prominence, but a depression. The third sacral spine 

 is on a level with the posterior superior spines of the ilium. The level at which the spinal cord 

 terminates should be known to the surgeon if he proposes to tap the spinal theca (lumbar punc- 

 ture] for diagnostic or therapeutic purposes or for spinal anesthesia. In an adult the cord terminates 

 at the lower border of the first lumbar vertebra, and the theca terminates opposite the body of the 

 third sacral vertebra. In a young child the cord terminates opposite the body of the third lumbar 

 vertebra, and the theca ends at about the same level as in an adult. Hence, in either a child 

 or an adult, a puncture below the level of the fourth lumbar vertebra will inflict no injury upon 

 the cord. In children the puncture is made just beneath the spinous process, and in adults 

 about one-half an inch to either side of the spinous process, although the needle should be made 

 to enter the dura in the median line. In either case the needle is directed upward and forward. 

 As previously pointed out, the surgical anatomy of an infant's spine is not identical with the sur- 

 gical anatomy of an adult's spine. The umbilicus of an infant is opposite the body of the fourth 

 lumbar vertebra; in an adult it is opposite the spinous process of the third lumbar vertebra. 

 In an infant the base of the sternum is on a level with the top of the seventh cervical spine, and 

 in an adult of the second thoracic spine (A. H. Tubby). The vertebral column may be the seat 

 of tuberculosis, which may destroy the bodies of the vertebrae; in such cases a deflection of the 

 column may be directed either forward or backward. This deflection is produced by the great 

 weight of the trunk on the diseased bone. If the deflection is directed forward, it is called 

 lordosis; if backward, kyphosis. Scoliosis (lateral deviation of the vertebral column) is usually 

 due to a faulty attitude of children while standing or while sitting at school desks. 



Occasionally the coalescence of the laminae is not completed, and consequently a cleft is left 

 in the arches of the vertebra?, through which a protrusion of the spinal membranes (dura mater 

 and arachnoid), and sometimes of the spinal cord itself, takes place, constituting a malformation 

 known as spina bifida or hydrorhachitis. This condition is most common in the lumbosacral 

 region; but it may occur in the thoracic or cervical region, or the arches throughout the whole 

 length of the canal may remain unapproximated. In some rare cases, in consequence of the 

 noncoalescence of the two primary centres from which the body is formed, a similar condition 

 may occur in front of the canal, the bodies of the vertebra? being found cleft and the tumor 

 projecting into the thorax, abdomen, or pelvis, between the lateral halves of the bodies affected. 



The construction of the spinal column of a number of pieces, securely connected together 

 and enjoying only a slight degree of movement between any two individuals pieces, though 

 permitting of a very considerable range of movement, as a whole, allows a sufficient degree of 

 mobility without any material diminution of strength. The main joints of which the spine is 

 composed, together with the very varied movements to which it is subjected, render it liable to 

 spraim, which may complicate other injuries or may exist alone; but so closely are the individual 

 vertebrae articulated that these sprains are seldom severe, and an amount of violence sufficiently 

 great to produce tearing of the ligaments would tend to cause a dislocation or fracture. The 

 further safety of the column and its less liability to injury is provided for by its disposition in 

 curves instead of in one straight line. For it is an elastic column, and must first bend before 

 it breaks; under these circumstances, being made up of three curves, it represents three columns, 

 and greater force is required to produce bending of a short column than of a longer one that is 

 equal to it in breadth and material. Again, the safety of the column is provided for by the inter- 

 position of the intervertebral disks between the bodies of the vertebra?, which act as admirable 



