186 



ANIMAL PHYSIOLOGY. 



, in its loose coverings, in the 

 middle of which, it is re- 

 tained by the ligamenta 

 ad denticulata and the passage 

 outwards of its nerves, an 

 efficient protection which 

 accounts for its immunity 

 from damage in movements 

 of the vertebral column. The 

 brain, on the other hand, fits 

 exactly within the cavity of 

 the unyielding cranium. 



140. The Spinal Cord ex- 

 tends from the skull to the 

 level of the first lumbar ver- 

 tebra, and is from fifteen to 

 eighteen inches long. It is 

 about the thickness of the 

 little finger, but is broader 

 from side to side at the part 

 of the neck where the great 

 nerves pass off to supply the 

 arms, and presents another 

 thickening at its lower end, 



Fig. 97. SPINAL CORD. A, 

 Transverse section in cervical 

 region ; a r, anterior root of 

 epinal nerve ; p r, posterior 

 root ; g, spinal ganglion ; a d, 

 anterior division of nerve; pd, 

 posterior division. B, Front 

 view of a portion in the dorsal 

 region, with the dura mater 

 laid open, and the anterior 

 roots of nerve on the right 

 side divided; I I, ligamentum 

 denticulatum. C, Front view 

 of the extremity of the cord 

 and part of the cauda equina. 

 The roots of the nerves are 

 divided on the left side; ft, 

 filum terminale. The arachnoid 

 is omitted in these figures, 



