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Chapter 7. ANATOMY AND MORPHOLOGY OF THE CHICKEN Some features of the domestic chicken ( Gallus domesticus ) will be noted to highlight the similarities and, more importantly, the differences between this avian species and the mammals with which most of this book is concerned. There is considerable anatomic variation among the domesticated birds, including chickens, turkeys, ducks, and geese, but the domestic chicken is by far the most important agricultural species and hence is chosen as the type species for this brief treatment of comparative anatomy. A. External anatomy and morphology The external form of the mature chicken (fowl) is very obviously different from that of the mammals that have been described. Disregarding for the moment those features that differ between sexes ( sexual dimorphisms ), the major regions and appendages of the chicken (Figure 7-1) include the head, neck, crop, breast, wing (forelimb), back, abdomen, uropygium, and leg. Because the leg (hindlimb) is relatively massive it is further classified into thigh, leg, hock, shank, and foot with the spur and claws. The body's additional appendages include combs, wattles, and ear lobes, which are highly vascularized, thick folds of skin; and the beak, spurs, claws, and plates on the shank, which are horny derivatives of the skin. Most striking in contrast to mammals is the complete absence of hair and its replacement over much of the body with Figure 7-1 . Morphology and external anatomy of the chicken. The external surface of the chicken is covered with an elaborate feather pattern that obscures the relationship between portions of the body, such as the neck, thorax, and abdomen. Note the accessory structures – comb, wattle, and spur – and the feather-free surface of the lower leg. 2007 version – page 47
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Figure 2-1. Beijing-You chickens. These small-framed birds are a popular local breed in China. The pattern of feathering is quite different to contemporary western breeds. The females (to the left and right) clearly show the “top-knot” of feathers and all birds have extensive feathering down the shank and onto the feet. Photo was kindly provided by Dr J. Wen, Institute of Animal Science, Chinese Academy of Agricultural Science, Beijing, PRC. feathers. Feathers take several distinct forms with differences in structure related to their function, and they are found in quite distinct tracts on the body. Color, length and distribution of feathers varies in different breeds and strains. The birds in Figure 7-2 are Beijing-You, a popular breed in China. Notice the “top-knot” of feathers, the
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This note was uploaded on 03/23/2009 for the course ANSCI 1110 taught by Professor Brucecurrie during the Fall '08 term at Cornell University (Engineering School).

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