LESSON 50.] NUTRITION IN THE MAMMALIA. 



LESSON L. 



NUTRITION IN THE MAMMALIA. 



767. The digestive organs vary more in this class than in any 

 other of the Vertebrated animals ; moreover, they present the high- 

 est type of development in the various organs connected with the 

 function of nutrition. 



768. The high condition of their organs of sense assist these 

 animals to perceive minuter differences in the chemical and physical 

 properties of their food ,' while the structure and fixed position of 

 the teeth enable them to comminute their aliment, and mix it suffi- 

 ciently with the secretion of the salivary glands, for the final pur- 

 poses of digestion. 



769. The Rodentia (gnawing) present some striking peculiarities 

 in connection with the development of their nutrimental organs. 

 Although possessing but one stomach, it 



contains, nevertheless, the elements of 



two very distinct organs. The stomach 



of the common Bat (Fig. 283) offers a 



good illustration ; the oesophagus (a) 



communicates with nearly the centre of 



the organ, and can, with the like ease, 



deposit food on either side. By inflating 



and drying such an illustration, a line of 



demarcation will then be visible, clearly stomach of the Eat 



dividing the organ into two distinct parts ; that towards the pylorus 



(6), on the right side as it lies in situ (d), will appear to be fhick^ 



as if composed (as in truth it is) of the three coats common to such 



an organ ; on the left side (e) there is superior transparency, and a 



number of lines, ridges, or furrows, transverse in their direction ; the 



duodenum commences at c. In the figure the organ is reversed, but 



it is everywhere described correctly. 



770. If, instead of inflating and drying the stomach, it be cut 

 open for examination, the left side (e) will be found devoid of mucous 

 membrane, or muscular coat ; both of which, together with an ex- 

 ternal serous coat, are found in connection with the right side (d). 

 To render our examination complete, we should try the injecting 

 syringe, to ascertain the vascularity of the organ, and here a very 

 interesting fact is disclosed : the right side of the stomach is in- 



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