Animal Morphology. 103 



in diffusion of their fibres from their spinal roots, they 

 occupy a common neural arch, or the posterior arch of the 

 notochord. 



On the other hand, the sense of want, elsewhere called 

 the hcemal sense, and giving consciousness both of suffoca- 

 tion and of hunger, occupies the anterior arch of the noto- 

 chord ; or, in other words, it is the true sense to the haemal 

 arch. 



In introducing to the notice of the reader the sense appa- 

 ratus pertaining to animal, as distinct from vegetable life, 

 a totally new order of membranous differentiation occurs, 

 and general metamorphosis ; the true transitionary mem- 

 brane being the mammary. And here a few general remarks 

 will be made. 



For the sake of uniformity, and perhaps also to make the 

 subject more simple, the plan of giving the three membranes 

 serous, mucous, and contractile will be adhered to ; and the 

 fourth division, a true animal nerve membrane, which in- 

 cludes sensation and motion, will be given as a sense for 

 which a tripartite membrane is supplied, to enable it to fulfil 

 its functions, and to obey the mandates of its requirements, 

 which proceed from the brain, or great emporium of all the 

 senses. But, rigidly speaking, the membrane of animal 

 life is a quaternary membrane, or a quadruple membrane, 

 and consists of nerves of sense and motion of a voluntary 

 character, and also of an involuntary character, one proceed- 

 ing from the spinal cord, and the other from the brain ; and, 

 in speaking of animal life membranes, they ought to be ex- 

 pressed as each membrane consisting of four divisions 

 nerve, contractile, serous, and mucous membrane. But, as 

 before said, nerve will always be understood, and each mem- 

 brane will be spoken of as a tripartite sense apparatus. 



So each special animal membrane is, as it were, nothing 

 more nor less than a series of mechanical appliances, here 



