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Revision as of 16:29, 3 November 2008

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[[Image:LH_Canine_labelled_ventrodorsal_abdominal_organs_radiograph.jpg|right|150px]]
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[[image: Parts of the Feather.jpg|thumb|250px|right|Parts of a Contour Feather:
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The spleen is a major lymphoid and blood filtration organ and is located in the left cranial abdomen. It is responsible for storing and removing [[Erythrocytes - WikiBlood|erythrocytes]] from the blood as well as antigen surveillance of the blood and antibody production.
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<br/>1. Vane<br/>2. Rachis<br/>3. Barb<br/>4. Afterfeather<br/>5. Calamus]]
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Feathers are one of the epidermal growths that form the distinctive outer covering, or '''plumage''' of birds. They are the outstanding characteristic that distinguishes the Class '''Aves''' from all other living groups.
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==Development==
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==Structure & Function==
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<p>The spleen develops in association with the digestive system in the dorsal mesogastrium, and as the [[Forestomach - Anatomy & Physiology|stomach]] rotates during development the spleen comes to occupy the left cranial abdomen. Haematopoietic cells in the spleen are derived from the AGM (aorta-gonad-mesonephros) and yolk sac and as the [[Primary Lymphoid Tissue - Anatomy & Physiology|primary lymphoid organs]] become established it becomes populated with [[Lymphocytes - WikiBlood#Types|T and B lymphocytes]].</p>
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'''Principal functions:'''
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==Structure==
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*Flight
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<p>The spleen lies vertically on the left side of the cranial abdomen. It is attached to the greater curvature of the [[Alimentary - Anatomy & Physiology#Stomach|stomach]] by the gastrosplenic ligament. The spleen is covered in a enclosed in a capsule of fibrous and elastic tissue that extends into the parenchyma as trabeculae.  </p>
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*Insulation
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<p> The parenchyma is supported by a fine mesh of reticular fibres and is divided into two types of tissue, the red and the white pulp. The red and white pulp are separated by the marginal sinus.</p>
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*Waterproofing
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'''Additional functions'''
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*Courtship displays
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*Defence
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Cryptic colouring (camouflage)
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Colour mimicking
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Dominance/subdominance conflicts
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*Aggressive territorial behaviour
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In most birds, the body is divided into areas that contain feather ''tracts'', '''pterylae''' and areas that do not, '''apteriae'''.  The location and the number of tracts varies between species. By originating from tracts rather than being randomly distributed, feathers can smoothly overlap and conform to the natural contours of the body.  By laying feathers over apteriae, air can be trapped beneath, providing [[Thermoregulation in Skin - Anatomy & Physiology|insulation]].
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The portions of the feather can be described as follows:
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*'''Calamus''': The short, hollow, tubular, unpigmented end of the mature feather inserted into the feather follicle and thus present below the skin level.
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*'''Rachis''': The long solid, tubular extension of the calamus above the skin. The rachis contains pith, which is composed of air-filled keratinised epithelial cells surrounded by a solid keratinised outer cortex.
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*'''Shaft''': The combination of the rachis and the calamus.
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*'''Vane or Vexillum''': The portion of the feather that extends to either side of the rachis and is composed of the barbs and their associated structures.  The vane is either '''plumulaceous''' (soft and downy) or '''pennaceous''' (compact and closely knit) depending on the individual type of feather.
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*'''Barbs''': The series of branches fused to the rachis, constituting the major surface area of the feather. Barbs also have branches called '''barbules''' which have hooks that lock the barbs together.
     
Jtulloch
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