6 MAMMALIAN ANATOMY 



waste products. Under certain conditions it divides to produce two 

 independent cells. 



Such are the general qualities of the original animal cell, but only 

 some of them are retained by the cells produced by segmentation. For 

 example, in those cells which are differentiated into cells of muscular 

 tissue contractility is supreme, and other functions are subordinate or 

 disappear ; in the cells of the nervous tissue the generation of nervous 

 impulse and the reception of sensation are supreme, but contractility 

 is lost. In other cells, such as gland-cells, food is worked over and 

 products are thrown out, as milk, saliva, or sweat. The red corpuscles 

 of the blood become oxygen-carriers for the other tissues. In many of 

 the connective tissues for example, bone the cell is subordinate to 

 its derivative, the intercellular substance ; in some epithelial tissues 

 there is but little intercellular substance, and the cells closely united 

 take on the functions of a membrane. 



PLAN OF THE BODY. 



The cat's body is constructed on the general mammalian plan. It 

 consists of a head and trunk supported by four limbs. A plane passing 

 through the long axis divides the body into right and left halves, and, 

 as one half is, in the main, similar to the other half, the body is said 



FIG. 2. 



Body Cavity. 



Mouth, 



Alimentary Canal.. ."SL? 



.Neural Canal. 



Lungs... ^5 



Thoracic Cavity.-' 



r_ h Alimentary Canal. 

 -- Abdominal Cavity. 



Diaphragm. 



PLAN OF VERTEBRATE BODY. 



to be bilaterally symmetrical. The end which terminates in the head 

 differs from the end which terminates in the tail. There are traces of 

 original construction which render possible a division of the body into 

 transverse segments, or metameres. Examples of these traces are the 

 segmentation of the vertebral column of the skeleton into vertebrae; 



