CHAPTER XL. 



THE MAMMALIA. 



THE Mammalia are warm-blooded viviparous animals that 

 suckle their young with milk from the mammary glands. The 

 members of this class differ considerably among themselves in 

 matters of detail, but in general the structure is the same, and 

 the processes are carried on in the same way throughout the 

 group. 



A good general idea of the class may be gained by the careful 

 study of some animal, as a rabbit, a cat, a puppy, or any other 

 that is convenient. A good knife and a saw are all the instru- 

 ments necessary, although a pair of forceps, and little hooks to 

 hold parts in position or out of the way are a great convenience. 

 First, go carefully over the external features of the animal, com- 

 paring it with others as far as possible. If not dead, kill it with 

 chloroform and open the body cavity for its whole length, cut- 

 ting a way the breast bone and a portion of the ribs. Notice the 

 diaphragm dividing the abdomen from the chest ; note the form 

 of the two cavities and the lining membrane of each. Study care- 

 fully the relative position of the organs in each cavity, turning 

 them over so as to find them all; do not hurry; try to see every 

 organ in its place, surrounded by its associated organs also in 

 place. Through a tube, inflate the lungs, trying to imitate the 

 breathing of the animal. Then study each organ and group of 

 organs somewhat in detail, so as to get, if possible, some idea of 

 how each organ performs its work. Study the heart carefully, 

 tracing out the distribution of the larger blood vessels. Open 

 the cranium ; notice the protective coverings of the brain, its di- 

 visions and external appearance. Find the origin of the nerves 

 of smell, sight, hearing and taste, and trace them to their respect- 



L. S.-20 (305) 



