DESCRIPTION OF THE PLATES \ 



PLATE I. 



Common Rat (Mus Decumanus), 



Dissected so as to show, superiorly, tlie cerebrospinal nervous system lodged in the 

 craniospinal cavity, and, inferiorly, portions of most of the organs of vegetative 

 life. 



The distinctive characteristic of the Vertebrate type, the pos- 

 session, namely, of an internal skeleton specially connected with 

 the organs and functions of animal life, is clearly shown in this 

 figure. The internal skeleton is seen forming a separate chamber 

 for the central nervous system which presides over motion and 

 sensation, apart from the larger cavity in which the organs of 

 vegetative life are lodged. By virtue of this arrangement Ver- 

 tebrata may be spoken of as ' Bicavitary ' animals, in contradis- 

 tinction to Invertebrata which are ordinarily ' Unicavitary."* Se- 

 condly, we see that it is the internal, and not as in Invertebrata 

 an external, skeleton which gives origin and support to the active 

 and passive organs of locomotion. Thirdly, the limbs, which are 

 never more in number than two pairs, are directed towards that 

 surface of the body in apposition with which the heart, the great 

 centre of the circulatory or haemal system, is placed (m). Hence 

 Vertebrata may be spoken of as ' Haemapods,' in contradistinction 



" The Description of the figure given in this plate will be found to coincide in 

 many particulars with the Descrijition given at pp. I-5 siq^-a of the first series of 

 Preparations. The Descriptions of plates vi. and vii. stand in a somewhat similar 

 relation to the Descriptions of the Preparations jo and 32. But in none of these 

 cases are the Descriptions mere repetitions, but will be found to be complementary of 

 each other. In the present Description, for example, the upper part of the figure 

 has been drawn from a dissection distinct from that described at pp. 1-5 supra; and 

 the structures lettered here f/ and y' will be found not to have been described before. 



