THE SPINAL CORD. 



SPINAL CORD. 



The spinal cord or spinal marrow (medulla spinalis) is about 18 inches (45 

 centimeters) long, and extends from the margin of the foramen magnum of the occi- 

 pital bone to about the lower part of the body of the first lumbar vertebra. Above, 

 it is continued into the bulb (medulla oblongata) ; below, it tapers conically and 

 ends in a slender filament, the ftlum terminate or central ligament of the spinal cord. 



Although the cord usually ends near the lower border of the body of the first 

 lumbar vertebra, its termination is sometimes a little above or below that point, as 



Fig. 2. SECTIONS SHOWING THE GENERAL RELATIONS OF THE SPINAL CORD TO THE INCLOSING THECA, 



AND OF THIS TO THE VERTEBRAL CANAL. (Key and Retzius.) 



A, through the fifth cervical vertebra ; B, through the tenth dorsal vertebra ; C, through the first 

 lumbar vertebra and the foramen of exit of the twelfth dorsal nerve-roots ; D, through the disk between 

 the second and third lumbar vertebrae ; E, through the first sacral vertebra. In A, B, and C, the cord, 

 covered by pia mater, is seen in the centre, with the ligamentum denticulatum attached to it on either 

 side ; the nerve-roots on either side form small groups which, since they pass obliquely downwards to 

 their foramina of exit, are cut across ; the dura matral sheath is separated by a considerable space from 

 the cord, and by a quantity of loose areolar and fatty tissue from the wall of the vertebral canal. This 

 tissue is in smaller amount in C. D and E are below the termination of the cord, and show sections of 

 the nerve-bundles of the cauda equina within the dural sheath, which is very large in D, but compara- 

 tively small in E, the vertebral canal in the latter being largely occupied by adipose tissue. In this are 

 seen the sections of two large veins. The arachnoid is not represented in any of these sections. 



opposite to the last dorsal or to the second lumbar vertebra. The position of the 

 lower end of the cord also varies according to the state of curvature of the vertebral 

 column, in the flexion forwards of which the end of the cord is slightly raised. In 

 the foetus, at an early period, the embryonic cord occupies the whole length of the 

 vertebral canal ; but, after the third month, the canal and the roots of the lumbar 

 and sacral nerves begin to grow more rapidly than the cord itself, so that at birth the 

 lower end reaches only to the third lumbar vertebra. After birth the thoracic part 

 of the cord lengthens proportionately more than the other parts, so that in the infant 

 the roots of the lower dorsal nerves come off relati velv higher up than at a later age 

 (Pfitzner). 



