AX ATOMY OF A BIRD. 249 



Mammalia, the Monotremata. In birds it is provided with a special glandular appendage on its 

 upper (or dorsal) aspect, which goes by the name of the Bursa Fabricii. Neither the history nor the 

 functions of this peculiar organ can be said to be thoroughly understood. 



Of the organs which are appended to the intestine, the lungs will be described elsewhere ; of 

 the rest we have to consider the liver, the pancreas, and the spleen. The first-named organ is large, 

 and covers over the pancreas, the proventriculus, the spleen, part of the gizzard, and part of the small 

 intestine. It is ordinarily divided into two " lobes," between which, on the upper edge, is placed the 

 tip of the heart. In the common fowl the left lobe is often divided into two ; but this organ is never 

 broken up into so large a number of parts as it is in many mammals, from which animals birds also 

 differ in always having more than one duct to carry off the secretion of the liver (bile) to the small 

 intestine, except in the Ostrich ; in this, as in some other birds, there is no gall-bladder in which the 

 bile may be collected, so that in such this secretion passes directly into the intestine. 



As has been already pointed out, the commencement of the small intestine forms a loop, in 

 which is set the organ known as pancreas, which may for simplicity be described as the salivary 

 gland of this region, although in truth the fluid secreted from it is a much moi-e powerful aid to the 

 digestion of food than that of any known salivary gland. It has always two, and in a number of cases 

 three ducts, which do not unite with the bile ducts, but open separately from, though near them, into 

 the end of the "duodenal loop." The spleen, which is a small oval body, and is placed to the 

 right of the proventriculus, has no ducts ; in birds of prey it is more cylindrical in shape. 



The temperature of the blood of the bird is, in requirement with the conditions of 

 its existence, hot that is to say, it is ordinarily hotter than the temperatui'e of the surrounding 

 air, and is found to register between. 100 (Gull) and 112 (Swallow) on Fahrenheit's scale, 

 or from two to fourteen degrees more than does that of man. Birds and mammals, are, 

 speaking broadly, the only hot-blooded animals now existing, and it has consequently beeiv 

 suggested that they should be grouped together as such, in opposition to the rest of the Ver- 

 tebi-ata. But it is obvious that this character of the temperature is merely dependent on 

 physiological conditions ; and were this a treatise on the anatomy of birds rather than one on their 

 natural history, the statement of this fact would not receive the prominence here given to it. The 

 high temperatm-e of any body may be preserved from cooling influences by two methods : thus, tea 

 in a well-polished silver teapot keeps hot because the rays of heat are but slightly radiated from its 

 surface ; or a less costly teapot may be kept hot by covering it with a loosely-fitting " cosy," which, 

 being made of badly -conducting materials, " keeps the heat in." It is, then, clear that the heat of 

 a body is best preserved when it is covered by a bad radiator and a bad conductor of heat ; and this 

 is just the case with birds : the polished feathers are bad radiators, and the air entangled among them 

 forms a bad conductor. 



The blood corpuscles are, broadly speaking, about twice as large as in man ; those which are 

 coloured red are oval in shape, as they are in nearly all of the lower Vertebrates and in the Camels 

 among mammals. Like the white ones, they are "nucleated." The heart is, as in mammals, 

 divided into four chambers. It is a condition of the circulation in hot-blooded and rapidly -breathing 

 animals that the current of arterial blood from the heart, and the current of venous blood to it, 

 .should be kept as much as possible separate ; no reflection is needed to show that the blood freshly 

 purified by contact with the air in the lungs must be kept as distinct as can be from the blood which 

 has lost its purity in passing through the body ; in other words, it is required that there should be a 

 similar result in birds and in mammals. 



Birds, like all warm-blooded creatures, have the heart divided into four cavities two ventricles 

 and two auricles those of the right side being completely separated from those of the left. The 

 whole is enclosed in a pericardium, a thin, but strong, membrane. The right ventricle has thin 

 muscular walls, and almost completely envelopes the left. The right auricle has a remarkable valve 

 in the shape of a fleshy leaflet, which appears almost to be a portion of the inside of the ventricle 

 that has become detached from the partition between the two ventricles. The blood, under certain 

 circumstances, passes between this septum, or partition, and the leaflet, into the auricle ; but when 

 the beat of the heart takes place (the systole), the septum, being convex, is forced against the leaflet 

 on the other side of the auricolo -ventricular opening, and the passage of the blood, through this, is 



