INTERNAL STRUGTUHE. 



11 



In the uppermost segments (upper part of the cervical enlargement) the grey 

 matter is again diminished in amount and the cord has become circular in outline, 

 as in the dorsal region. The section has however the other cervical characteristics, 

 and there is a much more strongly marked anterior commissure than in the thoracic 

 cord. Opposite the first cervical nerve-roots the cord begins to merge into the 

 medulla oblongata or spinal bulb, and the passage of the pyramidal fibres from the 

 pyramids on one side of the bulb to the lateral tracb on the other side of the cord 



Fig. 11. TRANSVERSE SECTIONS OF SPINAL CORD AT DIFFERENT HEIGHTS. (W. R. Gowers.) TWICE THE 



NATURAL SIZE. 



The letters and numbers indicate the position of each section : Go. at level of coccygeal nerve ; 

 Sac. 4 of 4tb sacral ; L3 of 3rd lumbar, and so on. The grey substance is shaded dark, and the nerve- 

 cells within it are indicated by dots. 



tends partially to obliterate the anterior median fissure and to cut up the grey 

 crescent. 



In the cervical region the nerve-roots leave the cord nearly at a right angle and 

 close together ; in the other regions at an angle which is more or less oblique, the roots 

 being directed from the intervertebral foramina upwards towards the cord ; in the 

 thoracic region they succeed one another at relatively longer intervals than 

 elsewhere. 



