NERVOUS SYSTEM. VERTEBRATA. 499 



medulla, and that the can da equina is formed by the nerves 

 after they have passed through the dura mater, as in the 

 Porpesse ; but here it may be observed that after they have 

 perforated the dura mater they do not run so obliquely 

 downwards [backwards], and therefore the cauda is not so 

 perfect." 



The crural swelling merges very gradually into the rest of 

 the cord in front. In the interspaces between the nerves 

 the arachnoid forms a series of lateral connections with the 

 dura mater the external attachments of a longitudinal 

 ligament (1. denticulatum) by which the cord is suspended 

 in the centre of the neural canal. 



0. C. 1365. Hunterian. 



D. 782. The spinal cord of a Giraffe (Qiraffa camelopardalis) 

 The dura mater has been removed except around the nerve- 

 roots. In the cervical region the nerves are widely sepa- 

 rated, but their tributary rootlets arise from so large an 

 area of the cord that the last rootlet of one nerve-root 

 arises almost on the same level as the first of the succeeding 

 root. The rootlets of the second cervical nerve are indicated 

 on the right side by the insertion of a black rod between 

 the sensory and motor series. The brachial and crural 

 swellings are slightly developed. 0. C. 1305 A. 



D. 783. The spinal cord of a Calf (Bos taurus). The dura 

 rnater has been longitudinally divided above and below and 

 reflected to either side. By this means the subdural space 

 and nerve-roots are well shown, as well as a series of pro- 

 cesses of the pia mater and arachnoid (ligamentum den- 

 ticulatum) , by which these membranes are laterally united 

 to the dura in the intervals between each pair of spinal 

 nerves. 



The arachnoid also accompanies the rootlets of the spinal 

 nerve-roots, and is at these points clearly distinguishable 

 from the underlying pia mater. 



In front of the crural swelling the cord has been folded 

 upon itself, and in this part the dura mater has not been cut. 

 The brachial and crural swellings merge very gradually 



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