THE NERVOUS SYSTEM 



in which the entire cord is perhaps a little shorter than the 

 brain. In all cases in which a shortening has occurred two con- 

 nected phenomena may be 

 observed at the posterior end 

 of the cord: first, the thick, 

 functional portion terminates 

 more or less abruptly and the 

 cord is continued as a taper- 

 ing thread known as the 

 filum terminate, without 

 function as a nervous organ, 

 and secondly, the shortening 

 is usually so great that the 

 posterior portion of the cord 

 is drawn up considerably 

 ahead of the parts which it 

 supplies, compelling the 

 nerves involved to turn 

 around at a progressively 

 sharper angle until the most 

 posterior ones run in a 

 longitudinal direction paral- 

 lel to the filum terminale. 

 This bundle of approximate- 

 ly longitudinal nerves which 

 appears thus to terminate 

 the cord, is known collective- 

 ly as the cauda equina, and is 

 often a noticeable object, as 

 in the frog and in Man 

 (Fig. 121, c). In the higher 

 vertebrates, especially in 

 mammals, the relation of 

 spinal cord to tail becomes 

 quite different from that of 

 the lower forms, a change 

 that is correlated in an inter- 



FIG. 121. Spinal cords, show- 

 ing the intumescentia, also a 

 marked length variation. 



(a) Turtle. [After BOJANUS.] (b) 

 Orthagoriscus (telecost). [From GEGEN- 

 BAUR after B. HALLER.] (c) Human 

 spinal cord without the brain. [After 



WlEDERSHEIM.] 



