502 PHYSIOLOGICAL SERIES. 



CETAOEA. 



" The medulla spinalis is much smaller in proportion to the size of 

 the body than in the human species, but still bears some proportion ! 

 the quantity of brain ; for in the Porpoise, where the brain is l:u 

 the medulla spinalis is largest; yet this did not hold good in the 

 Spermaceti Whale, the sixe of the medulla spinalis appearing to be 

 proportionately larger than the brain, which was small when compared 

 to the size of the animal .... The dura mater .... where il rovers 

 the medulla spinalis, differs from all the quadrupeds I am acquainted 

 with, inclosing the medulla closely, and the nerves immediately passing 

 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." 

 HUNTER, " Observations on the Structure and (Economy of Whales," 

 Phil Trans, vol. Ixxvii. 3787, p. 4lM. 



D. 791. The hinder part of the brain and the spinal cord of a 

 Porpoise (Pkoccena phocccna). 



" The dura mater is removed from about one half of the 

 breadth of the posterior surface [on the left side] through 

 its whole length to expose the medulla. It is not so loose 

 as in the Human subject, but incloses the medulla very 

 tightly. It goes no further than to the lower end of the 

 medullary substance ; so that it does not inclose the cauda 

 equina beyond that termination, as in tbe Human subject 

 or Monkey. The nerves go out of this sheath immediately, 

 through the whole length of the medulla ; so there is no 

 cauda equina on the inside of the dura mater either above 

 or below the termination of the medullary substance. The 

 cauda equina is therefore on the outside of the sheath of 

 the duni muter." 



Although in a sense the strands of the cauda equina and 

 the distal parts of the other nerve-roots may be said to lie 

 outside the dura, if by that we mean the common dural 

 investment of the cord, yet each root from its emergence 

 from this common investment to its exit from the neural 

 canal is covered by a reflexion of the dura, and thus in fact 

 lies within it. The cervical region of the cord is remarkably 

 short. The nerves in this part are consequently aggregated 

 together, the hindermost arising from a fairly pronounced 



