DIGESTION 



■s.r.\ 



From rr, which is a branch of the facial nerve named the chorda tympani, 

 it will be observed, two sets of fibres emanate, one going directly to the 

 cells of the gland, the other to the artery. Those to the artery cause it 

 to dilate and so allow a 

 freer current of blood to 

 circulate in and around the 

 gland; the other stimu- 

 lates the gland cells them- 

 selves to secrete, and thus 

 leads to an abundant flow 

 of saliva. These nervous 

 impulses ceasing with the 

 swallowing of the food, 

 the sympathetic centre re- 

 sumes its supremacy and 

 contracts the blood-vessels; 

 then secretion ceases, to be 

 resumed once more when 

 sapid substances are again 

 introduced into the mouth. 

 The thorough mingling 

 of the saliva with the food 

 is termed insalivation, and 

 the process is of great im- 

 portance and is very per- 

 fectly accomplished in all 

 herbivora. The horse 

 chews its food leisurely, 

 and a large quantity of 

 saliva is poured forth. 

 Observations and experi- 

 ments have been made 

 which show that this ani- 

 mal takes from an hour 

 to an hour and a half 

 to eat 6 lbs. of hay, and 

 more than half an hour 



to eat the same weight of oats. It makes about two hundred boluses, 

 or separate masses for swallowing, of the hay; and from forty to ninety 

 boluses of the oats. The weight of the dry hay is increased during 

 mastication from 6 lbs. to no less than 25 lbs., and of the oats from 



Fig. 81.— Abdo 



Laid Open 



A, Posterior or abdominal aorta. V, Posterior vena cava. U, U, 

 Ureters. R K, Right kidney. L K, Left kidney. D, Duodenum. 

 Pa, Pancreas. Sp, Spleen. ' St, Stomach. LL, Left lobe of liver. 

 ML, Middle lobe. RL, Right lobe. 



