556 



APPENDIX. 



terminates about the twenty-fifth vertebra, beyond 

 which is the cauda equina, the dura mater going 

 no lower. The nerves which go off from the 

 medulla spinalis are more uniform in size than in 

 the quadruped, there being no such inequality of 

 parts, nor any extremities to be supplied, except 

 the fins. The medulla spinalis is more fibrous in 

 its structure than in other animals ; and when 

 an attempt is made to break it longitudinally, it 

 tears with a fibrous appearance, but transversely it 

 breaks irregularly. The dura mater lines the skull, 

 and forms in some the three processes answerable 

 to the divisions of the brain, as in tlie human sub- 

 ject ; but in others this is bone. Where it co- 

 vers the medulla spinalis, it differs from all the 

 quadrupeds I am acquainted with, inclosing the 

 medulla closely, and the nerves immediately pass- 

 ing out through it at the lower part, as they do at 

 the upper, so that the cauda equina^ as it forms, 

 is on the outside of the dura mater. 



The cutis in this tribe appears, in general, 

 particularly well calculated for sensation ; the 

 whole surface being covered with villi, which are 

 so many vessels, and we must suppose, nerves. 

 Whether this structure is only necessary for acute 

 sensation, or whether it is necessary for common 

 sensation, where the cuticle is thick and consist- 

 ing of many layers, I do not know. We may 

 observe, that where it is necessary the sense of 

 touch should be accurate, the villi are usually 

 thick and long, which probably is necessary, be- 

 cause in most parts of the body, where the more 



