50 



two fingers and a thumb, one of which is very much larger than the other, and 

 consists of two or three joints. 



I will not delay longer upon this part of the anatomy of birds, as in the 

 next section I shall have to describe the wing more particularly, and I will pass 

 on to notice that portion of the internal organisation of birds which is most 

 specially adapted to the requirements of flight. 



Internal Anatomy. 

 "With regard to the digestive organs I will only notice that birds possess 

 similar i)arts to mammals, but that the intestinal tube, from the gullet to the 

 pylorus, presents considerable diversities, there being present, generally speaking, 

 two enlargements of the oesophagus, one called the crop, and the other, which is 

 just above the gizzard, the proventriculus. In both of these receptacles the food 

 is mixed with juices which accelerate digestion. 



The stomach or gizzard, as it is called, is a very peculiar oi'gan, and is, 

 in fact, a sort of grinding mill, where the food which enters it is ground down. 

 Tlie cavity of the stomach is very small, and the muscles which surround it are 

 very large. 



The intestines are variable in length, and do not present any marked 

 division into large and small intestines. They receive, as in mammals, the 

 secretions from the liver and the pancreas. 



With the above brief notice I wiU pass on to the organs of respiration, 

 which as clearly as anything in nature, show the marks of a designing hand. 



The lungs of birds are of a lengthened oval shape, and are firmly attached 

 to the dorsal surface of the thorax ; they are not divided into lobes, and from 

 each lung proceeds a bronchial tube, which tubes unite together to form the 

 trachea, or wind pipe, and it is at the junction of the bronchial tubes that the 

 lower larynx, where the vocal sounds of birds are produced, is placed. 



The main ti-unks of the bronchii after passing tliroiigh the lungs open 

 into the cavity of the thorax, and admit the air freely all through the body, for 

 in birds there is no proper diaphragm, but the whole of the thoracico abdominal 

 cavity is divided into cells which communicate with each other, all of which are 

 freely permeated by the air, which therefore surrounds all the vital organs, and 

 penetrates in many cases into the interior of the bones and muscle. 



The bones which are most commonly found hollow and pneumatic in birds, 

 are the humerus, or arm bone, the breast bone, and the cranial bones. Some- 

 times, however, the other bones are found so also. 



The pneumatic bones receive their air from the air-sacs which are 

 connected with the lungs; but the cranial and facial bones receive their air partly 

 from the Eustachian tubes, partly from the tympanic c.ivity, and partly from 

 the nasal cavities which conducts it to spaces under the eyes, whence it pene- 

 trates further into the bones of the skull. 



