186 PHYSIOLOGY AT THE FARM. 



Its form is for the most part globular, somewhat com- 

 pressed ; it consists of four muscles possessed of great strength 

 and thickness. Of these, two occupy the sides, having fibres 

 running around two tendons, also on the sides of the organ. 

 The other two muscles, smaller than the former, are placed at 

 the opposite extremities of the stomach. 



The gizzard has among its outer coats a tendinous expan- 

 sion lined by a thick strong callous coat, regarded by some as 

 a continuation of the cuticle. This inner layer forms irregu- 

 larities on its inner side, which, on the opposite surfaces, adapt 

 themselves to each other. Compared to its external surface, 

 the inner surface is very small, while its two orifices are sin- 

 gularly near each other. 



The great thickness of the gizzard is supposed to compen- 

 sate for the defect of teeth in birds. Such statements as the 

 following are cited in proof of its great power : that pieces of 

 money, and even pebbles of the hardest sort, swallowed by a 

 fowl, have lost a considerable part of their weight within a few 

 days ; that a silver thimble swallowed by a young turkey was 

 taken from its gizzard a few days after with its sides squeezed 

 together. Each of the small muscles at the ends of the giz- 

 zard forms a kind of receptacle for the small stones habitually 

 swallowed, in order to separate them from the digested food 

 which passes on to the intestines. 



The muscularity of the gizzard is at its maximum in gran- 

 ivorous birds ; in carnivorous birds it is at its minimum. 



A parroquet and some other birds have been thought to 

 chew the cud like ruminant quadrupeds. The name spurious 

 rumination has been sometimes applied to the effect produced 

 on food by the hard and callous gizzards of poultry and geese. 



The swan and the palmipedes for the most part have a giz- 

 zard approaching in muscularity to that of the gallinaceous 

 birds. 



