82 Animal Morphology. 



is, in mammalia at least, the lowest form of tissue, and in 

 the series of differentiations from primordial cells to brain 

 tissues it is the lowest and most diffuse general tissue, 

 which serves as general servant to all the membranes. 



In true Mammalia it may be affirmed that they have ten 

 membranes of a tripartite character. 



Firstly : The abdominal viscera and glands generally from 

 mouth to anus, consisting of serous, muscular, and mucous 

 membrane, constitute but one tripartite membrane the in- 

 flections of mucous membrane in the form of glands, as 

 Brunner's, Peyer's, liver, pancreas, etc., being included as 

 parts of the abdominal mucous membrane, and outside a 

 second, or serous membrane, with unstriped muscle be- 

 tween as a third membrane. 



Secondly : The broncho-plural membrane, with its minute 

 and limited bronchial terminal muscular coat, but in some 

 mammalia not purely constrictors or sphincters to the 

 air cells, for they extend here and there to the larger 

 bronchi. 



Thirdly : The genito-urinary membrane. 



Fourthly : The mammary system. 



Fifthly : The lacteo-lymphatic system. 



Sixthly : The musculo-osseous system. 



Seventhly : The brain and arachnoid. 



Eighthly: The veno-arterial system, or circulating system. 



Ninthly : The ganglionic system. 



Tenthly : The integument, which is viewed as a compound, 

 or tripartite membrane. 



These systems, or tripartite membranes, are most com- 

 pletely interlocked with each other, and also they are 

 capable of the widest and most varied conditions of trans- 

 position. 



The first membrane of a tripartite character, as here 

 maintained, is the alimentary canal and its appendages. 



