ANIMAL KINGDOM. 277 



compose the spine. The nerves communicate with this me- 

 dullary trunk by holes in the vertebrae and skull, and there 

 appear all to unite in a double medullary band, which, after 

 having crossed its filaments, spreads itself in order to form 

 the different tubercles of the brain, and to terminate in the 

 two medullary hemispheres of which the volume generally 

 corresponds with the extent of intelligence. 



As the vertebrated spine is the distinguishing mark of 

 these animals, it is evident that the imperfection of this cha- 

 racter will always point out the particular species by which 

 we are to leave the group. The bones, as we have seen in the 

 Cephalopoda and Reptiles, were at first represented by carti- 

 lages; we naturally look therefore for those other vertebrated 

 animals which have their skeleton particularly cartilaginous. 

 The Chondropterygian fishes have the calcareous matter 

 deposited in their skeleton by small grains and not by fibres 

 or filaments. The articulations gradually disappear in these 

 animals, and in the Lampreys we find the spine composed 

 of one solid cartilage upon which the last trace of articula- 

 tion appears as wrinkles. Fins and every other vestige of 

 limbs or members are here at last totally lost. An elon- 

 gated body is terminated by a fleshy circular or semicir- 

 cular lip, and the cartilaginous ring which supports this 

 lip results from the palatines and mandibles being soldered 

 together. The branchiae, instead of being formed of la- 

 mina? as in other fish, have the appearance of purses or 

 bags, resulting from the union of the face of one pair 

 with the opposite faces of its neighbour. We are arrived, 

 in fine, at animals, such as the genus Ammocatus of Du- 

 meril, where the skeleton is soft and membranaceous, or 

 as the genus Gastrobi^anchus or Myxine, where no trace 

 of the eye exists, where the maxillary ring itself becomes 



