THE ANATOMY OF BIRDS.— FNEU3IAT0L0GY. rj9 



Both limbs of birds have n prime peculiarity of their arteries as compared with mammals. 

 In the fore limb, the Wood supply beiug ehietly absorbed by the hnmeiisc pectoral muscles, 

 vessels which iu mamuials are small axiUary branches appear like the ujaiu continuation of the 

 suhdaoian trunk, and the brachial arteries are correspondingly reduced. In the leg, the main 

 source of supply is the great ischiac artery, the femoral beiug small. This ischiac artery cor- 

 respouds to the twig which in nniu accompanies tlie great sciatic nerve {comes mroi ischinfici) ; 

 and the rare human anomaly of a jjosfcrior main vess(d of tlie thigh is therefore a I'eversion 

 (atavism) to the avian rule. There is no single proper renal artery to the kidney. 



The Lymphatics of Ijirds consist cliietly of a deep set accompanying the main blond- 

 vessels, forming various jjfexus, —nodes, "glands," (jr "lymph-hearts" in their course. Su- 

 perficial lymphatics, so prominent in mammals, are little developed, though lymphatic gland,s 

 are found in the arm-pit and groin of some birds. These are the s?/s(<>HiiC vessels; a siiecial 

 set, the lacfeals, arise by numberless twigs iu the course of the small intestine, uniting and re- 

 uniting to form at length turn (not one as in mammals) main tubes, which lie along either side 

 of the spinal column. These are the thoracic fhicts: which terminal trunks of the whole lym- 

 phatic system empty into tlie right and liA't, jufjiilar veins at the root of the neck. The contents 

 of the vessels differ correspondingly. Pure lymph is a, pale, limpid, allmminous fluid, contain- 

 ing when maturely elaborated a number of irregular amo'boid bodies, indistinguishable from 

 the white formative corpuscles of the blood (p. 196). Tt is strained out of the tissues at large, 

 lieiug that material, not yet effete, which is still fit for feeding the blooil. Tlie lacteals contain 

 ch,jle,—the other kind of lymph, drained oft' liy the mucous membrane of tlie intestine from the 

 prepared food in that tube ; an albuminous fluid, milky or cloudy from the abundance of oil- 

 globules, which, after mingling with the systemic lymph, is ijoured (Urectly into the current of 

 the blood, iu the manner above said. Since the lacteals do not ajjpear to begin with open 

 mouths, the chyle must soak into them through the lining membrane of the intestines; and 

 as this consists of a layer of amoeba-like animals, through whose bodies the chyle passes, it is 

 cpiite true to say that the whole organism is nourished upon the excrement of amcebas- 



e. Pneumatology : the Respiratory System. 



The Organs of Respiration provide for the ventilation of the body. Since the respii'a- 

 tory process is also calorific, they likewise furnish a heating apparatus. They consist essen- 

 tially of air-passages and air-spaces connected with lung-tissue, being therefore pulmonary 

 organs. No other animals are so thoroughly permeated as birds with the atmospheric medium 

 in which they live ; in no others are the respiratory functions so energetic and effectual. The 

 lung may be likened ti.> a blast-furnace for the combustion of decayed animal matter ; purifica- 

 tion of the blood and warming of the body beiug two inseparable results obtained. Dark 

 blood flowing to the lungs, heavy with eft'ete carbonaceous matters, is there relieved of its bur- 

 den and aerated by the action of oxygen ; the products of combustion being exhaled in the 

 form of carbonic dioxide aud water. Aside from the proper lung-tissue, the capillary substance 

 of the immense air-sacs tends to the same result. There is likewise, in birds, a lesser system 

 of ventilation, by which air is admitted to cranial bones through the eustachian tubes; but 

 this is unconnected with the proper respiratory office. Pulmonary tissue consists chiefly of a 

 wonderful net (a rete mirahile) of capillaries, interlacing in every direction, bound together and 

 supported by fine connective tissue, and invested with membrane so delicate that their walls 

 seem naked, their exposure to the air beiug thus very tliorongh. Air gains such intimacy 

 with the capillaries through the larynx, trachea (fig. 101, o), and bronchial tubes {r, r), these 

 being the primary air-passages. But all the bronchial tubes do not subdivide into the ultimate 

 air-cells; some large ones run through the lung, pierce its surface (as at u, a. fig. 101), and end 



