398 ANATOMY AND PHYSIOLOGY OF THE SPINAL CORD. 



the cord, at the point where the sensory roots of the spinal 

 nerves are connected with it ; the latter extend downward 

 and outward towards the anterior roots, but stop short 

 before reaching the surface. The inferior columns are still 

 further connected by a portion of white matter extended 

 across, between the grey commissure and the inferior median 

 fissure. This is the white commissure of the cord. The 

 cord is not of a uniform diameter throughout. Its dimen- 

 sions vary according to the number and size of the nerves 

 which originate from any particular point ; as, for example, 

 in those parts which correspond to the lower end of the 

 neck and the posterior part of the loins, it presents two 

 considerable enlargements, from which originate the great 

 nervous trunks of the anterior and posterior limbs. The 



Fig. 211. Transverse section of the spinal cord and its membranes, a, Inferior aspect; 

 p, superior aspect; n, nerve; 1, dura mater; 2, 3, outer and inner layers of arachnoid; 

 4, pia mater; 5, ligamentum denticulatum ; 6, arachnoid cavity; 7, subarachnoid space. 



weight of the cord in middle-sized animals is, according to 

 Chauveau in the horse, 75 J- dr. (300 grammes); in the 

 donkey, 38 dr. ; in the cow, 55 dr. ; in the sheep and goat, 

 770 gr. ; in the, pig, 1078 gr. ; in the dog, 539 gr. ; in the 

 cat, 123 gr. ; and in the rabbit, 77 gr. 



The spinal cord does not fill up the whole spinal canal. 

 The latter contains, besides, a large venous sinus, fatty 

 matter, the membranes of the cord, and the cerebro-spinal 



