1198 SURFACE AND SURGICAL ANATOMY. 
Spinal Cord.—The spinal cord ends opposite the lower border of the first 
lumbar spine; in the infant it reaches to the interval between the second and 
third lumbar spines. The cervical enlargement which corresponds to the lower 
four cervical and the first two dorsal segments ends opposite the seventh cervical 
spine. The /wmbar enlargement lies opposite the last three dorsal spines. The 
five lumbar segments are opposite the ninth, tenth, and eleventh dorsal spines, 
while the five sacral segments extend from the lower border of the eleventh dorsal 
to the lower border of the first lumbar spine. 
The sub-dural space extends down to the level of the second sacral spine. In 
performing the operation of /wmbar puncture (Quincke) a fine trochar and cannula 
is introduced into the subarachnoid space below the level of the cord, the puncture 
being made } to $ in. to one side of the interspinous ligament in the interval 
between the third and fourth or fourth and fifth lumbar spines. The instrument 
should be directed inwards towards the mesial plane and very shghtly upwards. 
In the adult the distance of the thecal sac from the surface is about 2 in., in the 
infant # in. 
Fracture-dislocations of the spine are commonest in the lower cervical and 
dorso-lumbar regions; that is to say, where the movable cervical and lumbar 
regions join the more fixed dorsal region. The spinal column above the injury 
is generally displaced forwards, so that the spmal cord is often severely lacerated 
or completely torn across by the upper end of the portion of the column below 
the fracture. It is important to remember that in consequence of the shortness 
of the cord as compared with the spine, the origins of the spinal nerves are at a 
higher level than their exits from the spinal canal. The distance between. their 
origins from the cord and their exits through the intervertebral foramina becomes 
ereater the further down we descend, the lowest nerve trunks running almost 
vertically downwards. The cervical nerves leave the spinal canal above pe 
vertebre after which they are named; the dorsal, lumbar, and sacral nerves, ¢ 
the other hand, leave the canal below the correspondingly named vertebree. 
To understand the effect of lesions of the cord, it is necessary to be familiar with 
the sensory and motor distributions of the various spinal segments (see Figs. 422, p. 569, and 
424, p. 573). Transverse lesions of the cord above the fifth cervical spine (that is, above 
the disc between the fourth and fifth cervical vertebrie) are quickly fatal from paralysis of 
respiration, as the phrenic nerve arises mainly from the fourth segment. In transverse 
lesions of the cervical enlargement the cutaneous insensibility does not extend higher than a 
transverse line at the level of the second intercostal space. The diagnosis of the particular 
segment involved is arrived at by testing the motor and sensory functions of each segment. 
The sensory areas corresponding to the lower four cervical and ‘the Jirst two dorsal segments 
occupy the upper extremities, and are placed in numerical order from the radial to the 
ulnar side of the limb. The sensory area corresponding to the second, third, and fourth 
cervical segments occupy the occipital region of the scalp, the back of the auricle, and 
the masseteric region, the whole of the neck, and the shoulders and upper part of the 
chest down to a horizontal line at the level of the anterior end of the third intercostal 
space. In total transverse lesion of the cord in the dorsal region, the upper limit of the 
anesthesia is horizontal, and reaches to the level of the terminations of the anterier primary 
divisions of the spinal nerves which arise from the spinal segment opposite the vertebral 
injury. Hence the upper limit of the anzesthesia is at a much lower level than that of the 
injured vertebra. or example, a fracture-dislocation at the level of the eighth dorsal 
vertebra involves the origin of the tenth dorsal nerve which ends at the level of the 
umbilicus. The sensory zone corresponding to the fifth dorsal segment is at the level 
of the nipples, that of the seventh dorsal segment is at the level of the ensiform cartilage, 
that of the tenth at the level of the umbilicus, while that of the twelfth reaches down 
anteriorly to the upper border of the symphysis. The sensory areas corresponding to 
the lumbar and sacral segments are seen in Figs. 422 and 424. 
THE UPPER EXTREMITY. | 
THE SHOULDER. 
The bony landmarks of the shoulder must be sy stematically examined in all 
injuries about this region. The inner extremity of the clavicle is prominent ; its 
