190 PHYSIOLOGY AT THE FARM. 



kidneys, the ends of the vasa deferentia or seminal ducts in 

 the male sex, and also the penis when it exists, the opening of 

 the oviduct in the female, and the orifices of the bag named 

 " bursa Fabricii/' The cloaca has a variety of forms in differ- 

 ent species, but its appearance nevertheless is more or less of 

 an oval shape. In both sexes it serves as a reservoir of urine 

 and faeces. Its movements are directed by several muscles, 

 which arise from the adjacent bones. At the upper and back 

 part of the opening into it in both sexes is situated the bursa 

 Fabricii. In some large birds, as in the goose, it is more than 

 an inch long, with its cavity lined by mucous glands. It is 

 proportionally of greater size in young birds, while in old birds 

 it is very much contracted. It is uniformly found empty, and 

 its use has not yet been discovered. 



In birds in general there is no omentum, unless the lump 

 of fat covering the intestines in some aquatic fowls be regarded 

 as representing that structure. In the ostrich there is an 

 omentum, with a large quantity of fat. 



, The Liver. In birds the liver is proportionately larger than 

 in mammals. It has a more uniform figure. It is for the most 

 part divided into two almost equal lobes, and these are rarely 

 very unequal. It occupies both the right and left hypochondriac 

 regions, and even a great part of that portion of the common 

 cavity which corresponds to the chest in mammals. The great 

 size of the liver in birds seems to correspond with what is com- 

 monly received respecting the functions of that organ and their 

 relation to the functions of the lungs. 



It might seem that such an organ should decline in import- 

 ance, and consequently in size, in proportion as a tribe of 

 animals has an augmented respiration ; but it may be answered 

 that in birds there cannot be too many means of augmenting 

 the proportion of oxygen in the blood, since the great activity 

 of movement in flight requires the greatest possible irritability 



