AVES. 



347 



Barn-Owl (Strix jlammea) and Horn-Owl 

 (Otus aurita). The influence of these muscles 

 upon the voice must obviously be in proportion 

 as they shorten the bronchi and depress the 

 lower larynx, according to the different inser- 

 tions above mentioned. 



A further degree of complexity in the organ 

 of voice is presented by the Psittacida or Par- 

 rot-tribe, which, according to Cuvier, have three 

 pairs of inferior laryngeal muscles. 



The Insessores, lastly, present five pairs of 

 muscles appertaining to the lower larynx, and the 

 organ of voice consequently attains its greatest 

 perfection in this order. ' 



The peculiar structure of the lower larynx, 

 and the modifications of the trachea in relation 

 to its functions, will be treated of under the 

 article Organs of Voice. 



Urinary Organs. These consist in birds of 

 the kidneys, ureters, and a urinary receptacle, 

 which is more or less developed in all birds. 



The kidney of the oviparous vertebrate ani- 

 mal is distinguished from that of the mammi- 

 ferous by the homogeneity of its substance, 

 which is not divided into a cortical and medul- 

 lary part, and by the tubuli uriniferi extending 

 to the surface of the gland there to form by 

 reiterated unions the ureter, and not terminating 

 in a cavity or pelvis in the interior of the kidney, 

 from which the ureter commences. 



The kidneys (x x, Jig. 182) of birds manifest 

 all the essential characters of the oviparous type 

 of structure. They are two in number, of an elon- 

 gated form, commencing immediately below the 

 lungs, and extending along the sides of the spine 

 as far as the termination of the rectum ; in which 

 course they are impacted in, and as it were 

 moulded to the cavities and depressions of the 

 pelvis. From this fixed condition it results that 

 they are generally symmetrical in position, not 

 placed one higher than the other, as in the mam- 

 malia. The posterior surface of the kidney pre- 

 sents inequalities corresponding to the risings 

 and depressions of the pel vis; the anterior sur- 

 face is smoothly convex or flattened ; but rising 

 into a series of prominences which correspond, 

 not to the eminences, but to the cavities of the 

 bones on which they rest : their inner or mesial 

 side is generally pretty regular and straight, but 

 the external edge is more or less notched. 



From the nature of the integuments about to 

 be described, and the small amount of cutane- 

 ous transpiration in birds, the office of removing 

 from the system the superfluous watery part of 

 the circulating fluids devolves almost exclu- 

 sively upon the kidneys, and they are conse- 

 quently relatively larger than in the terrestrial 

 mammalia. 



The kidneys vary in size in different birds, 

 being for example smaller in most of the 

 Grallatores, as the Bustard and Heron, where 

 the pelvis is short, than in the Rasorial 

 Order, in which it is of great extent. Where 

 they are short they are in general more promi- 

 nent, and this is so remarkable in some birds, 

 as the Owls, that in them they resemble some- 

 what in their superficial position the kidneys of 

 mammalia. 



As might be expected from their relations 

 to the pelvis, the kidneys in birds present as 

 many varieties of outward configuration as 

 there are differences in the part of the skeleton 

 to which they are moulded. In some aquatic 

 birds, as the Grebe ( PodicepsJ and the Coot 

 (Fulica), the kidneys are more or less 

 blended together at their lower extremities, as 

 in most fishes. In the rest of the class they are 

 distinct from one another. 



In the Tern they are each divided by fissures 

 into seven or eight square-shaped lobes. In 

 the Eagle they each present four divisions ; but 

 in these cases there are not distinct ureters to 

 each lobe as in the subdivided kidneys of mam- 

 malia. 



The principal lobes are in general three in 

 number, the anterior or highest one being, in 

 some cases, the largest; while in others, as 

 the Pelecan, the contrary obtains, the lowest 

 division being most developed in this bird. 



In the Emeu ( Dromaius ater) the kidney 

 presents only two lobes; the superior or anterior 

 one is the broadest and most prominent, being 

 of a rounded figure, and constituting one-third 

 of the whole ; the lower division is flattened, 

 and gradually tapers to a point. In the speci- 

 men we dissected we found the left kidney half 

 an inch longer than the right. 



Each kidney is invested by its proper capsule, 

 a thin membrane, which also extends into the 

 substance of the gland, between its divisions : a 

 delicate layer of peritoneum is reflected over 

 their anterior surfaces. 



The texture of the kidneys is much more frail 

 than in mammalia, readily yielding under the 

 pressure of the finger, to which they give a granu- 

 lar sensation as their substance is torn asunder. 



In colour they resemble the human spleen. 

 Besides being divided into lobes, the surface of 

 the kidneys may be observed to be composed of 

 innumerable small lobules, separated by conti- 

 nuous gyrations like the convolutions of the 

 cerebral substance. The ultimate divisions of 

 the lobules and their intimate structure can 

 only be distinguished by observations on the 

 embryo, unless when the component follicles 

 are filled, as they occasionally are seen to be 

 after death, with the white salts of the urinary 

 secretion. The tubuli urinij'eri, as Miiller ob- 

 serves,* may then be seen under the microscope 

 originating from every part of the internal sub- 

 stance of the lobules, extending to the gyrations, 

 uniting in the pinnatifid form, and coursing to 

 the margins of the lobules, all the inflexions of 

 which they follow. The pinnatifid ramification 

 of the uriniferous tubules is sometimes opposite, 

 sometimes alternate. Sometimes the branches 

 are simple, sometimes dichotomously divided : 

 but these ramuli appear scarcely smaller than 

 the branches from which they spring, and never 

 intercommunicate. They have been successfully 

 injected with size and vermilion, without any 

 of this material escaping into the secerning 

 vessels, which are much more minute. The 

 uriniferous ducts, when thus traced from the 



* De Glandularum Structura, p. 92. 



