22 POULTRY DISEASES 



metatarsus terminates inferiorly with three artieuhir sur- 

 faces or facets which articulate with the three principal digits, 

 (49), (50) (53). A conical eminence is noted near the inferior 

 third which turns hackwards and is the base of the spur. ^lost 

 fowls have four digits. The os metatarsale or rudimentary 

 digit (51) projects backward and is made up of three pha- 

 langes. The second or internal toe (49) is provided with three 

 phalanges, the third or middle toe (53) is provided with four 

 phalanges, and the external or fourth toe (50) is jorovided 

 with five phalanges. 



VISCERAL ANATOMY OF THE HEN 



THE DIGESTIVE TRACT 



Mouth 



The mouth cavity is characterized by the changing of the 

 jaw bones into the beak. There are no teeth. The tongue is 

 shaped like an Indian arrow, with prominent, rather hard 

 and sharp pointed papillae, along its posterior border. 



There is an upper and lower beak. The upper beak is pro- 

 vided with sharp free edges. There are no lips or cheeks. 

 The upper jaw forms the base of the upper beak, and the 

 lower jaw forms the base of the lower beak. The beaks are 

 covered by a continuation of the epidennis. The beak is 

 formed of horn-like material that is rather hard and resists 

 wear to which it is subjected. 



In many water birds, as geese and ducks, a thin dermoid 

 structure is formed over the edges of the beak, in which 

 numerous branches of the trigeminus terminate in taste buds. 



In chickens the beak terminates in a sharp point, while 

 in water birds, as geese and ducks, the beak is flat, spatula- 

 like, and grooved transversely at its free margin. The roof 

 of the mouth (hard palate) is provided with a slit that ex- 

 tends antero-posteriorly, and is about one inch in length ; 

 this is the posterior nares. There are on the hard palate four 

 or more cross bars, each of which is provided with hard fili- 

 form papillae that point backward. The tongue presents a 

 flat surface superiorly, and is covered by a thick strata of 

 corneous epithelium. The dorsum (upper surface) is pro- 

 vided Avitli many small Aliform papillae, that point back- 

 wards. The ])ody of the tongue is made up of muscles and 

 connective tissue. The tongue of swinnning birds is thinner 

 tlian that of chickens. The tongue is an organ ])ossessing 

 both of the senses, taste and touch. The transverse I'ow of 

 filiform papillae of the posterior portion of the roof of the 



