Till-: N/'/A'.LA Ml It VEX 903 



men in ires, especially the dura, t lie nerve-roots and the trunk are attached to the peri- 

 osteum of the margins of the interverte! intl foramina and thus arc enabled to give 

 some lateral support to the -pinal cord in the upper portion of the ."anal. The 

 majority of the spinal iran.u'lia lie in the intervcrtebral foramina, closely cnsheal lied. 

 and I hi is outside the actual sac or cavity of the dura mater. The ganglia of the last 

 lumbar and lirM four sacral ncr\ cs lie inside t he vertebral canal, but since the. shea) h 

 derived from the dura mater closely adheres to them, they are still outside the sac of 

 the dura mater. The ganglia of the last sacral and of the cnccygcal nerves ("when 

 present) lie in tubular extensions of the sulxlural cavity, and thus not only within 

 the \crtebral canal, but actually within t he sac of the dura mater. The trunk of the 

 lirst cervical nerve is assembled within the sac of the dura mater, and, therefore, the 

 spinal ganglion of this nerve, when present, may lie within the sac. 



Course and direction of emergence. Invested with the connective-tissue 

 sheath derived from the meniimes. each spinal nerve emerges from the vertebral canal 

 through the inlervcrtebral foramen below the corresponding vertebra, and in re- 

 lation with the spinal rami of the arteries and veins associated with the blood supply 

 of the given localities of the spinal cord. The first cervical nerve does not pass out- 

 wards in an intervertebral foramen proper, but between the occipital bone and the 

 post erii >r arch of the atlas and beneat h t he vertebral artery. Thus the eighth or last 

 cervical nerve emerges between the seventh cervical and the first thoracic vertebra. 



The first and second pairs of cervical nerves pass out of the vertebral canal al- 

 most at right angles to the levels of their attachment to the spinal cord. During the 

 early periods of development the level of exit of each pair of spinal nerves is opposite 

 the level of its attachment to the cord, but, owing to the fact that in the later periods 

 the vertebral column grows more rapidly than the cord and increases considerably in 

 length after the cord has practically ceased growing, all the spinal nerves, with the 

 exception of the first two, pass downwards as well as outwards. The obliquity of 

 their course from the level of attachment to the level of exit increases progressively 

 from above downwards, and, as the cord terminates at the level of the second lumbar 

 vertebra, t he roots of the lower lumbar and of the sacral nerves pass at first vertically 

 downwards within the dura mater, and form around the filum terminale a tapering 

 sheaf of nerve-roots, the cauda equina (horse's tail) (fig. 566, p. 759). 



Topography of attachment. The relations between the levels of attachment of 

 the spinal nerves to the cord and the spinous processes of the vertebrae situated 

 opposite these levels have been investigated by Nuhn and by Reid. The following 

 table compiled by Reid gives the extreme limits of attachment as observed in six 

 subjects. 



TABLE or TOPOGRAPHY OF ATTACHMENT OF SPINAL NERVES. (Reid.) 



(A) signifies the highest level at which the root filaments of a given nerve are attached 

 to the cord, and (13) the lowest level observed. For example, the root filaments of the sixth 

 thoracic nerve may he attached as high as the lower border of the spinous process of the second 

 thoracic vertebra, or some may be attached as low as the upper border of the spinous process of 

 the fifth thoracic vertebra, but in a given subject they do not necessarily extend either as high 

 or as low as either of the levels indicated. 



Nerves 

 Second cervical (A) A little above the posterior arch of atlas. 



(B) Midway between posterior arch of atlas and spine of axis. 

 Third (A) A little below posterior arch of atlas. 



(B) Junction of upper two-thirds and lower third of spine of axis. 

 Fourth (A) Just below upper border of spine of axis. 



(B) Middle of spine of third cervical vertebra. 

 Fifth (A) Just below lower border of spine of axis. 



(B) Just below lower border of spine of fourth cervical vertebra. 

 Sixth (A) Lower border of spine of third cervical vertebra. 



(B) Lower border of spine of fifth cervical verl 

 Seventh ' (A) Just below upper border of spine of fourth cervical vertebra. 



(B) Just above lower border of spine of sixth cervical vend mi. 

 Eighth (A) Upper border of opine of fifth cervical vertebra. 



(B) Upper border of (pine of seventh cervical vertebra. 

 Fir.st thoracic (A) Midway between spines of fifth cervical and sixth cervical vertebra. 



(B) Junction of upper two-thirds and lower third of interval between seventh 



cervical and first thoracic vertebra. 

 Second (A) Lower border of spine of sixth ceivical vertebra. 



(B) Just above lower border of spine of first thoracic vertebra. 



