دستگاه تناسلی ماکیان و پرندگان ماده

دو گناد و اویدوکت متقارن دو طرفه در رویان پرندگان رشد و تکامل می یابند.عموما در پرندگان و به هر حال درتمام گونه های اهلی تخمدان وایدوکت چپ رشد وتکامل سریع تر ازقرینه خود در سمت راست دارند.در بسیاری از گونه ها در دوران بلوغ فقط اعضای سمت چپ جنس ماده فعال هستند اگر چه گاهی بقایای گناد واویدوکت راست باقی می ماند.بسیاری از پرندگان شکاری ومرغ کیوی قهوه ای در میان انواعی ازپرندگان هستند که غالبا دوتخمدان کاملا تکامل یافته دارند اگر چه تخمدان های راست وچپ در پرندگانی نیز متعلق به دست کم 16راسته دیده شده اند که معمولا فقط یک تخمدانی فرض می شوند.وجود دواویدوکت معمولا کمتر رخ میدهد اما در پرندگان شکاری به طور عمده پدیدار می شوند.در مرغ کیوی قهوه ای که دو تخمدان فعال دارد گزارش شده که ایدوکت چپ منحصر به فرد این پرنده برای دریافت اووسیت ازهر دو تخمدان چپ وراست به طور خاصی قرار گرفته است.
در بیشتر پرندگان بنظر می رسد که عمل وشکل کلی تخمدان واویدوکت چپ به طور شایان توجهی ثابت ودایمی است.


تخمدان چپ
(شکل و رشد)


در مراحل اولیه رشد رویانی در پیدایش جنس ماده ژنتیکی از ماکیان اهلی و چندین نمونه گونه های بی شمار دیگر در ناحیه گنادی سلول های جنسی مهاجر به طور نا برابر وارد شده که بیشتر به گناد چپ وارد می شوند تا گناد راست. این ناموزونی اولیه با مهاجرت بسیاری از سلول های جنسی از گناد راست به چپ زیاد تر می شوند. بنابراین حتی پیش از خروج از تخم گناد چپ بزرگتر از گناد راست می شوند.


سلول های جنسی نخستین به بافتی به نام بافت پوششی زاینده می پیوندند و سلول های دیگر بافت پوششی منشاٌ مزانشیمی(صفاقی) دارند. در ماکیان اهلی در طول روز های ششم و هفتم دوره نهفتگی (خوابیدن روی تخم)،بافت پوششی زاینده،رشته های جنسی اولیه را در اعماق گناد جوانه می زند که ناحیه مرکزی تخمدان در جنس ماده و لوله های ایجاد کننده اسپرم در جنس نر را بوجود می اورد.در جنس ماده ژنتیکی،بافت پوششی زاینده به ناحیه خارجی ضخیم از سلول ها تکثیر می یابد که این ساختار از رشته های جنسی اولیه به وسیله ی لایه ای از بافت همبند به نام لایه آلبوجینای اولیه جدا می شود.


در طول روز های هشتم تا یازدهم دوره نهفتگی این ناحیه خارجی ضخیم از سلولها تکثیر می کند و توده ثانویه سلول های ناحیه رویش پایینی رسته های ثانویه به وجود می اید.این سلول ها اووگونیا را تشکیل می دهند.اووگونیوم،سلول جنسی است که به طور فعال تکثیر می کند.هنگام توقف اووگونیوم ها از تکثیر،بزرگ شدن انها اغاز شده و به اووسیت های اولیه تبدیل می شوند.این فرایند در زمان خروج از تخم انجام می گیرد و در این مرحله،به پروفاز از نخستین تقسیم بلوغ(کاهش کروموزمی)می رسند.در این زمان بخش زیادی از محتویات زرده روی هم انباشته می شود و اووسیت اولیه بتدریج به اندازه ی کامل خود می رسد.اووسیت اولیه پرندگان،بزرگترین سلول در سلسله حیوانات است.در ماکیان اهلی وزن نهایی ان نزدیک به 20 گرم است.یکی از بزرگترین سلول های موجود در این سیاره،اووسیت مربوط به پرنده فیل ماداسگار بود که قطری نزدیک به 37 سانتی متر و حجمی به گنجایش یک سطل داشته است.تخمهای بزرگ این پرنده نابوده شده،احتمالاً اساس افسانه سیمرغ غول پیکر بوده است.در پایان دوره رشد،اووسیت ها دو تقسیم بلوغ خود را تکمیل می کنند.نخستین تقسیم،اووسیت ثانویه و دومین تقسیم،تخمک را به وجود می اورد.بنابراین سه مرحله اووژنز وجود دارد.یک دوره تکثیر،یک دوره رشد و یک دوره بالغ شدن.


در ماکیان اهلی از زمان بیرون امدن از تخم تا حدود 4 ماه پس از ان تخمدان چپ بتدریج و اهسته رشد می کند و طول ان به حدود 5/1 سانتیمتر،و وزن ان نزدیک به 5/0 گرم می رسد.در طول این مرحله ،تخمدان بخش قشری و مرکزی را در بر میگیرد..بخش قشری تخمدان ناحیه مرکزی را بجز بخشی از تخمدان را در بر می گیرد که در ارتباط با دیواره ناحیه پشتی بدن است.سطح خارجی قشری به وسیله استر پوششی مکعبی بلند و یا سلول های پوششی پهن صفاقی پوشیده شده است که تا بلوغ باقی می مانند.در زیر لایه پوششی،لایه ای از بافت همبند متراکم به نام لایه البوجینای مشخص کننده وجود دارد.بین 18 تا 24 هفتگی میزان رشد بسرعت افزایش می یابد،و بسیاری از اووسیت ها به بزرگترین اندازه خود می رسند و تمایز بین بخش قشری و مرکزی کاملاٌ از بین میرود.در این زمان نواحی پارانشینی نا مشخص با فولیکولهای نابالغ بسیاری نمایانگر ناحیه قشری و نواحی عروقی نا منظم در برانده عروق خونی،اعصاب،عضلات صاف و سلول های بینا بینی نمایانگر ناحیه مرکزی را در بر میگیرند.در اخرین مرحله رشد در طول 6 روز ضخامت اووسیت اولیه بالغ از 6 میلیمتر به حداکثر 40 میلیمتر افزایش می یابد که در این زمان وزن تخمدان نزدیک به 60 گرم بوده که به وسیله بند تخمدان معلق است، منطقه گسترده ای در بخش بالایی حفره شکمی را اشغال می کند و کلیه ها و ریه ها را می پوشاند.


نژاد های سبک ماکیان اهلی در 5 ماهگی و نژاد های سنگین در 6 تا 7 ماهگی به تخم می آیند. اما هیبرید های جدید را می توان پس از چهارو نیم ماهگی به تخمگذاری ترغیب کرد. بیشتر پرندگانی که تولید مثل فصلی دارند در نخستین بهار و یا در برخی گونه ها در دومین بهار پس از تخمگذاری زادوولد می کنند. اما برخی پرندگان از نظر جنسی بسیلر دیرتر ازاین زمان فعال می شوند. به عنوان مثال فولمارها نزدیک به 8 سالگی زادوولد را آغاز می کنند. از سوی دیگر سهره راه راه استرالیایی می تواند فقط پس از چند ماه زادوولد کند و به این ترتیب از دوره های بارندگی محدود بیشترین بهره را به دست می آورد و بلدرچین ژاپنی در قفس در 6 هفتگی از نظر جنسی فعال می شود خصوصیتی که ارزش این پرنده را به عنوان جانوران آزمایشگاهی بالا می برد.


در طول فعالیت جنسی تخمدان چپ به دلیل فولیکولهای بزرگی که از آن آویزان هستند همانند یک خوشه انگور است. در مرغهایی که به طور فعال تخمگذاری می کنند نزدیک به 4 ویا 5 فولیکول بسیار بزرگ با قطر 4 میلیمتر و به همین ترتیب هزاران نمونه کوچکتر آن نیز ممکن است پدیدار شوند. در طول دوره استراحت اندازه تخمدان چپ کاهش می یابد و در ماکیان اهلی فقط 2 تا 6 گرم است. در پرندگانی که تولید مثل فصلی دارند به طور کلی سه مرحله در تخمدان قابل تشخیص است. مرحله ی دوره فعالیت تخمدان که در این مرحله تخمدان بزرگ می شود مرحله جفت گیری که تخمکگذاری و تخمگذاری انجام می شود و سر انجام دوره استراحت که اندازه تخمدان بسیار کاهش می یابد. این مراحل کم و بیش با مراحل قابل مقایسه در بیضه ها همزمان هستند و سیستم ترشحی نوراندو کرین همانند جنس نر انها را کنترل می کنند.


تخمدان در ماکیان اهلی معمولا به وسیله خون سرخرگی شاخه تخمدانی لوله رحمی از سرخرگ کلیه ای قدامی چپ تامین می شود. خون تخمدان به وسیله دو سیاهرگ تخمدانی مستقیما به سیاهرگ میانخالی خلفی می ریزد. این رگهای خونی و بسیاری از اعصاب به سطح پشتی پهن تخمدان و ناف تخمدانی واقع در بالای حفره شکمی وارد می شوند.

قس

Bird anatomy, or the physiological structure of birds' bodies, shows many unique adaptations, mostly aiding flight. Birds have a light skeletal system and light but powerful musculature which, along with circulatory and respiratory systems capable of very high metabolic rates and oxygen supply, permit the bird to fly. The development of a beak has led to evolution of a specially adapted digestive system. These anatomical specializations have earned birds their own class in the vertebrate phylum.
Contents [show]
[edit]Skeletal system



A stylised dove skeleton. Key:
1. skull
2. cervical vertebrae
3. furcula
4. coracoid
5. uncinate processes of ribs
6. keel
7. patella
8. tarsometatarsus
9. digits
10. tibia (tibiotarsus)
11. fibia (tibiotarsus)
12. femur
13. ischium (innominate)
14. pubis (innominate)
15. illium (innominate)
16. caudal vertebrae
17. pygostyle
18. synsacrum
19. scapula
20. lumbar vertebrae
21. humerus
22. ulna
23. radius
24. carpus
25. metacarpus
26. digits
27. alula
The bird skeleton is highly adapted for flight. It is extremely lightweight but strong enough to withstand the stresses of taking off, flying, and landing. One key adaptation is the fusing of bones into single ossifications, such as the pygostyle. Because of this, birds usually have a smaller number of bones than other terrestrial vertebrates. Birds also lack teeth or even a true jaw, instead having evolved a beak, which is far more lightweight. The beaks of many baby birds have a projection called an egg tooth, which facilitates their exit from the amniotic egg.
Birds have many bones that are hollow (pneumatized) with criss-crossing struts or trusses for structural strength. The number of hollow bones varies among species, though large gliding and soaring birds tend to have the most. Respiratory air sacs often form air pockets within the semi-hollow bones of the bird's skeleton.[1] Some flightless birds like penguins and ostriches have only solid bones, further evidencing the link between flight and the adaptation of hollow bones.[citation needed]


Air-sacs and their distribution
Birds also have more cervical (neck) vertebrae than many other animals; most have a highly flexible neck consisting of 13-25 vertebrae. Birds are the only vertebrate animals to have a fused collarbone (the furcula or wishbone) or a keeled sternum or breastbone. The keel of the sternum serves as an attachment site for the muscles used for flight, or similarly for swimming in penguins. Again, flightless birds, such as ostriches, which do not have highly developed pectoral muscles, lack a pronounced keel on the sternum. It is noted that swimming birds have a wide sternum, while walking birds had a long or high sternum while flying birds have the width and height nearly equal.[2]
Birds have uncinate processes on the ribs. These are hooked extensions of bone which help to strengthen the rib cage by overlapping with the rib behind them. This feature is also found in the tuatara Sphenodon. They also have a greatly elongate tetradiate pelvis as in some reptiles. The hindlimb has an intra-tarsal joint found also in some reptiles. There is extensive fusion of the trunk vertebrae as well as fusion with the pectoral girdle. They have a diapsid skull as in reptiles with a pre-lachrymal fossa (present in some reptiles). The skull has a single occipital condyle.[3]
The skull consists of five major bones: the frontal (top of head), parietal (back of head), premaxillary and nasal (top beak), and the mandible (bottom beak). The skull of a normal bird usually weighs about 1% of the birds total bodyweight. The eye occupies a considerable part of the skull and is surrounded by a sclerotic eye-ring, a ring of tiny bones that surround the eye. This characteristic is also seen in reptiles.
The vertebral column consists of vertebrae, and is divided into three sections: cervical (11-25) (neck), Synsacrum (fused vertebrae of the back, also fused to the hips (pelvis)), and pygostyle (tail).
The chest consists of the furcula (wishbone) and coracoid (collar bone), which two bones, together with the scapula (see below), form the pectoral girdle. The side of the chest is formed by the ribs, which meet at the sternum (mid-line of the chest).
The shoulder consists of the scapula (shoulder blade), coracoid (see The Chest), and humerus (upper arm). The humerus joins the radius and ulna (forearm) to form the elbow. The carpus and metacarpus form the "wrist" and "hand" of the bird, and the digits (fingers) are fused together. The bones in the wing are extremely light so that the bird can fly more easily.
The hips consist of the pelvis which includes three major bones: Illium (top of the hip), Ischium (sides of hip), and Pubis (front of the hip). These are fused into one (the innominate bone). Innominate bones are evolutionary significant in that they allow birds to lay eggs. They meet at the acetabulum (the hip socket) and articulate with the femur, which is the first bone of the hind limb.
The upper leg consists of the femur. At the knee joint, the femur connects to the tibiotarsus (shin) and fibula (side of lower leg). The tarsometatarsus forms the upper part of the foot, digits make up the toes. The leg bones of birds are the heaviest, contributing to a low center of gravity. This aids in flight. A bird's skeleton comprises only about 5% of its total body weight
[edit]Birds feet


Types of bird feet
Birds feet are classificated as anisodactyl, zygodactyl, heterodactyl, syndactyl or pamprodactyl.[4] The first is the most common arrangement of digits in birds, with three toes forward and one back. This is common in songbirds and other perching birds, as well as hunting birds like eagles, hawks, and falcons.
Syndactyly, as it occurs in birds, is like anisodactyly, except that the third and fourth toes (the outer and middle forward-pointing toes), or three toes, are fused together, as in the Belted Kingfisher Ceryle alcyon. This is characteristic of Coraciiformes (Kingfishers, Bee-eaters, Rollers, and relatives).
The zygodactyly (from Greek ζυγον, a yoke) is an arrangement of digits in birds, with two toes facing forward (digits 2 and 3) and two back (digits 1 and 4). This arrangement is most common in arboreal species, particularly those that climb tree trunks or clamber through foliage. Zygodactyly occurs in the parrots, woodpeckers (including flickers), cuckoos (including roadrunners), and some owls. Zygodactyl tracks have been found dating to 120-110 Ma (early Cretaceous), 50 million years before the first identified zygodactyl fossils.[5]
Heterodactyly is like zygodactyly, except that digits 3 and 4 point forward and digits 1 and 2 point back. This is found only in trogons, while pamprodactyl is an arrangement in which all four toes may point forward, or birds may rotate the outer two toes backward. It is a characteristic of swifts (Apodidae).
[edit]Muscular system



The supracoracoideus works using a pulley like system to lift the wing while the pectorals provide the powerful downstroke
Most birds have approximately 175 different muscles, mainly controlling the wings, skin, and legs. The largest muscles in the bird are the pectorals, or the breast muscles, which control the wings and make up about 15 - 25% of a flighted bird’s body weight. They provide the powerful wing stroke essential for flight. The muscle medial (underneath) to the pectorals is the supracoracoideus. It raises the wing between wingbeats. The supracoracoideus and the pectorals together make up about 25 – 35% of the bird's full body weight.
The skin muscles help a bird in its flight by adjusting the feathers, which are attached to the skin muscle and help the bird in its flight maneuvers.
There are only a few muscles in the trunk and the tail, but they are very strong and are essential for the bird. The pygostyle controls all the movement in the tail and controls the feathers in the tail. This gives the tail a larger surface area which helps keep the bird in the air.
[edit]Integumentary system

See also: Beak, Comb (anatomy), Lore (anatomy), and Gular skin


Ostrich foot integument (podotheca).
[edit]Scales
The scales of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and metatarsus, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of kingfishers and woodpeckers. The scales and scutes of birds are thought to be homologous to those of reptiles and mammals.[6]
Bird embryos begin development with smooth skin. On the feet, the corneum, or outermost layer, of this skin may keratinize, thicken and form scales. These scales can be organized into;
Cancella – minute scales which are really just a thickening and hardening of the skin, crisscrossed with shallow grooves.
Reticula – small but distinct, separate, scales. Found on the lateral and medial surfaces (sides) of the chicken metatarsus. These are made up of alpha-keratin.[7]
Scutella – scales that are not quite as large as scutes, such as those found on the caudal, or hind part, of the chicken metatarsus.
Scutes – the largest scales, usually on the anterior surface of the metatarsus and dorsal surface of the toes. These are made up of beta-keratin as in reptilian scales.[7]
The rows of scutes on the anterior of the metatarsus can be called an acrometatarsium or acrotarsium.
Feathers can be intermixed with scales on some birds' feet. Feather follicles can lie between scales or even directly beneath them, in the deeper dermis layer of the skin. In this last case, feathers may emerge directly through scales, and be encircled at the plane of emergence entirely by the keratin of the scale.[6]
[edit]Rhamphotheca and Podotheca
The bills of many waders have Herbst corpuscles which help them detect prey hidden under wet sand using minute pressure differences in the water.[8] All extant birds can move the parts of the upper jaw relative to the brain case. However this is more prominent in some birds and can be readily detected in parrots.[9]
The region between the eye and bill on the side of a bird's head is called the lore. This region is sometimes featherless, and the skin may be tinted, as in many species of the cormorant family.
The scaly covering present on the foot of the birds is called podotheca.
[edit]Respiratory system

Further information: Lung#Avian lungs


Air always flows from right (posterior) to left (anterior) k through a bird's lungs during both inhalation and exhalation. Key to a Common Kestrel's circulatory lung system: 1 cervical air sac, 2 clavicular air sac, 3 cranial thoracic air sac, 4 caudal thoracic air sac, 5 abdominal air sac (5' diverticulus into pelvic girdle), 6 lung, 7 trachea
Birds ventilate their lungs by means of air sacs. These sacs do not play a direct role in gas exchange, but act like bellows to move air continuously one-way through the fixed volume lungs.[1] The evolution of this system helped birds achieve the high metabolic rate and high oxygen requirement required for strenuous flight, particularly at high altitude. Lungs are inevitably squeezed during locomotion using four legs, making fixed-volume lungs hard to evolve,[10] but birds had bipedal ancestors.
Three distinct sets of organs perform respiration—the anterior air sacs (interclavicular, cervicals, and anterior thoracics), the posterior air sacs (posterior thoracics and abdominals), and the constant-volume lungs. Unlike mammals, diving birds use a special mechanism to prevent lung crushing even at depths of over 300m.[11]


Birds' lungs obtain fresh air during both exhalation and inhalation
The posterior and anterior air sacs, typically nine, expand during inhalation. Inhaled air passes through the trachea and then the main (primary) bronchi mostly into the posterior air sacs but some goes directly to the lungs; most air that enters the lung on inhalation was shown by Bretz and Schmidt-Nielsen's classic experiments[12][13] to be air left in the posterior sacs from the previous cycle—sucked out of the rear sacs even during their expansion, and displaced by freshly inhaled air! On exhalation, air from the anterior air sacs and the lungs empties directly into the main bronchi, and out of the bird's mouth or nares via the trachea. The posterior air sacs pass air into the lungs on both inhalation and exhalation. Some taxonomic groups (e.g. Passeriformes) possess 7 air sacs, as the clavicular air sacs may interconnect or be fused with the cranial thoracic air sacs.
As air flows through the air sac system and lungs, there is no mixing of oxygen-rich air and oxygen-poor, carbon dioxide-rich, air as in mammalian lungs. Thus, the partial pressure of oxygen in a bird's lungs is the same as the environment, and so birds have more efficient gas-exchange of both oxygen and carbon dioxide than do mammals. In addition, air passes through the lungs in both exhalation and inspiration.
Avian lungs do not have alveoli, as mammalian lungs do, but instead contain millions of tiny passages known as parabronchi, connected at either ends by the dorsobronchi and ventrobronchi. (Click here then in ref below for diagram:;[14] the laterodorsal “secondary bronchi”, which are actually parabronchi in structure, link many large vessels at the rear of the lung in most birds. This confused mass of LDSB is called the neopulmo, and differs strikingly from the fairly neat arrangement of parabronchi in the main part of the lung called the paleopulmo. See [11] for an exploration of its utility.) Each parabronchus communicates with its surrounding honeycomb of air chambers—atria—each of which leads via a handful of large air capillaries known as infundibula (sing: infundibulum), to the richly interconnecting net of air capillaries proper.[11][15][16][17][18] Each atrium is globular-shaped, suggesting rotational air convection or at least turbulence is used in them, between the parabronchi with their directional flow, and the diffusion-using air capillaries. At the capillary level an effective countercurrent exchange does exist[10] for the oxygen and carbon dioxide diffusing along the air capillaries to be traded with counter-flowing capillary blood as it travels in towards the airway at the core of the parabronchus—the lumen. Air capillaries wiggle, merge and branch extensively, as do blood capillaries, and the two often, indeed usually, cross each other at right angles; Makanya et al.[19] though, do not yet accept that the net behaviour of a countercurrent system containing crosscurrent elements in this way, is still that of a countercurrent. The benefit of this appears to be lost though when blood capillaries from the oxygen-rich end of the parabronchi mix their blood with the contents of capillaries from the other end. There is a cross-current arrangement between air in the parabronchi and blood in the larger blood-vessels of the lung but the significance of these geometries is not yet fully understood. There are muscles around the edges of the atria where they meet the lumen, and carbon dioxide detectors near the start of parabronchi, whose function is currently unknown.
Birds lack a simple diaphragm but have a complex system of internal septa instead. The entire body cavity acts as a bellows to move air through the lungs. The active phase of respiration in birds is exhalation, requiring muscular contraction.
The syrinx is the sound-producing vocal organ of birds, located at the base of a bird's trachea. As with the mammalian larynx, sound is produced by the vibration of air flowing through the organ. The syrinx enables some species of birds to produce extremely complex vocalizations, even mimicking human speech. In some songbirds, the syrinx can produce more than one sound at a time.
[edit]Circulatory system

Birds have a four-chambered heart, in common with humans, most mammals, and some reptiles (namely the crocodilia). This adaptation allows for an efficient nutrient and oxygen transport throughout the body, providing birds with energy to fly and maintain high levels of activity. A Ruby-throated Hummingbird's heart beats up to 1200 times per minute (about 20 beats per second).[20]
[edit]Digestive system



Alimentary canal of the bird exposed.
Many birds possess a muscular pouch along the esophagus called a crop. The crop functions to both soften food and regulate its flow through the system by storing it temporarily. The size and shape of the crop is quite variable among the birds. Members of the order Columbiformes, such as pigeons, produce a nutritious crop milk which is fed to their young by regurgitation. Birds possess a ventriculus, or gizzard, composed of four muscular bands that rotate and crush food by shifting the food from one area to the next within the gizzard. The gizzard of some species contains small pieces of grit or stone swallowed by the bird to aid in the grinding process of digestion, serving the function of mammalian or reptilian teeth. The use of gizzard stones is a similarity between birds and dinosaurs, which left gizzard stones called gastroliths as trace fossils.
[edit]Drinking behavior
There are four general ways in which birds drink: using gravity itself, sucking, use of the tongue, and deriving water entirely from food.
Most birds are unable to swallow by the "sucking" or "pumping" action of peristalsis in their esophagus (as humans do), and drink by repeatedly raising their heads after filling their mouths to allow the liquid to flow by gravity, a method usually described as "sipping" or "tipping up".[21] The notable exception is the Columbiformes; in fact, according to Konrad Lorenz in 1939,
"one recognizes the order by the single behavioral characteristic, namely that in drinking the water is pumped up by peristalsis of the esophagus which occurs without exception within the order. The only other group, however, which shows the same behavior, the Pteroclidae, is placed near the doves just by this doubtlessly very old characteristic."[22]
Although this general rule still stands, since that time, observations have been made of a few exceptions in both directions.,[21][23]
In addition, specialized nectar feeders like sunbirds (Nectariniidae) and hummingbirds (Trochilidae) drink by using protrusible grooved or trough-like tongues, and parrots (Psittacidae) lap up water.[21]
Many seabirds have glands near the eyes that allow them to drink seawater. Excess salt is eliminated from the nostrils. Many desert birds get the water that they need entirely from their food. The elimination of nitrogenous wastes as uric acid reduces the physiological demand for water.[24]
[edit]Urogenital and Endocrine systems



Fledgling
Although most male birds have no external sex organs, the male does have two testes which become hundreds of times larger during the breeding season to produce sperm.[25] The testes in male birds are generally asymmetric with most birds having a larger left testis.[26] Female birds in most families have only one functional ovary (the left one), connected to an oviduct — although two ovaries are present in the embryonic stage of each female bird. Some species of birds have two functional ovaries, and the order Apterygiformes always retain both ovaries.[27][28]
In the males of species without a phallus (see below), sperm is stored in the semenal glomera within the cloacal protuberance prior to copulation. During copulation, the female moves her tail to the side and the male either mounts the female from behind or in front (as in the stitchbird), or moves very close to her. The cloacae then touch, so that the sperm can enter the female's reproductive tract. This can happen very fast, sometimes in less than half a second.[29]
The sperm is stored in the female's sperm storage tubules for a week to more than a 100 days,[30] depending on the species. Then, eggs will be fertilized individually as they leave the ovaries, before the shell is calcified (for species that produce hard shells) in the oviduct. After the egg is laid by the female, the embryo continues to develop in the egg outside the female body.


A juvenile Laughing Gull
Many waterfowl and some other birds, such as the ostrich and turkey, possess a phallus. The length is thought to be related to sperm competition.[31] When not copulating, it is hidden within the proctodeum compartment within the cloaca, just inside the vent.
After the eggs hatch, parents provide varying degrees of care in terms of food and protection. Precocial birds can care for themselves independently within minutes of hatching; altricial hatchlings are helpless, blind, and naked, and require extended parental care. The chicks of many ground-nesting birds such as partridges and waders are often able to run virtually immediately after hatching; such birds are referred to as nidifugous. The young of hole-nesters, on the other hand, are often totally incapable of unassisted survival. The process whereby a chick acquires feathers until it can fly is called "fledging".
Some birds, such as pigeons, geese, and Red-crowned Cranes, remain with their mates for life and may produce offspring on a regular basis.
[edit]Nervous system

See also: Bird vision and Avian pallium
Birds have acute eyesight - raptors have vision eight times sharper than humans - thanks to higher densities of photoreceptors in the retina (up to 1,000,000 per square mm in Buteos, compared to 200,000 for humans), a high number of optic nerves, a second set of eye muscles not found in other animals, and, in some cases, an indented fovea which magnifies the central part of the visual field. Many species, including hummingbirds and albatrosses, have two foveas in each eye. Many birds can detect polarised light.
Birds have a large brain to body mass ratio. This is reflected in the advanced and complex bird intelligence.
[edit]See also

List of terms used in bird topography
[edit]Notes

^ a b Ritchison, Gary. "Ornithology (Bio 554/754):Bird Respiratory System". Eastern Kentucky University. Retrieved 2007-06-27.
^ Ayhan Duezler, Ozcan Ozgel, Nejdet Dursun (2006) Morphometric Analysis of the Sternum in Avian Species. Turk. J. Vet. Anim. Sci. 30:311-314
^ Wing, Leonard W. (1956) Natural History of Birds. The Ronald Press Company. [1]
^ Proctor, N. S. & Lynch, P. J. (1998) Manual of Ornithology: Avian Structure & Function. Yale University Press. ISBN 0300076193
^ "Earliest zygodactyl bird feet: evidence from Early Cretaceous roadrunner-like tracks". Naturwissenschaften. 2007.
^ a b Lucas, Alfred M. (1972). Avian Anatomy - integument. East Lansing, Michigan, USA: USDA Avian Anatomy Project, Michigan State University. pp. 67, 344, 394–601.
^ a b Peter R. Stettenheim (2000) The Integumentary Morphology of Modern Birds—An Overview. American Zoologist 2000 40(4):461-477; doi:10.1093/icb/40.4.461
^ Piersma, Theunis; Renee van Aelst, Karin Kurk, Herman Berkhoudt and Leo R. M. Maas (1998). "A New Pressure Sensory Mechanism for Prey Detection in Birds: The Use of Principles of Seabed Dynamics?". Proceedings: Biological Sciences 265 (1404): 1377–1383. doi:10.1098/rspb.1998.0445.
^ Zusi, R L (1984). "A Functional and Evolutionary Analysis of Rhynchokinesis in Birds.". Smithsonian Contributions to Zoology 395. hdl:10088/5187.
^ a b Duncker, H-R. (2000). "Der Atemapparat der Vögel und ihre lokomotorische und metabolische Leistungsfähigkeit". Journal für Ornithologie. English summary 141: 1–67. Retrieved 16 July 2012.
^ a b c Jackson (2012). The Secret Dinobird Story. Amazon.
^ Bretz, W.L.; Schmidt-Nielsen, K. (1971). "Bird Respiration: Flow Patterns in the Duck Lung". J. Exp. Biol. 54: 103–118. Retrieved 16 July 2012.
^ Bretz, W.L.; Schmidt-Nielsen, K. (1972). "The Movement of Gas in the Respiratory System of the Duck". J. Exp. Biol. 56. Retrieved 16 July 2012.
^ Jackson. "Sub bronchi within bird lung". Fig. 7.3 from The Secret Dinobird Story. Amazon. Retrieved 18 July 2012.
^ Maina, J.N. (2000). "What it takes to fly: the structural and functional repsiratory requirements in birds and bats". The Journal of Experimental Biology 203: 3045–3064.
^ Maina, J.N.; West, J.B. (2005). "Thin and Strong! The Bioengineering Dilemma in the Structural and Functional Design of the Blood-Gas Barrier". Physiol. Rev. 85: 811–844.
^ Makanya, A.N.; Djonov, V. (2008). "Development and Spatial Organization of the Air Conduits in the Lung of the Domestic Fowl, Gallus gallus variant domesticus". Microscopy Research and Technique 71: 689–702. Retrieved 16 July 2012.
^ Woodward, J.D.; Maina, J.N. (2005). "A 3D digital reconstruction of the components of the gas exchange tissue of the lung of the muscovy duck Cairina moschata". Journal of Anatomy 206 (5): 477–492. Retrieved 16 July 2012.
^ Makanya, A.; El-Darawish, Y., Kavoi, B.M., Djonov V. (2011). "Spatial and Functional Relationships Between Air Conduits and Blood Capillaries in the Pulmonary Gas Exchange Tissue of Adult and Developing Chickens". Microscopy Research and Technique 74 (2): 159–169. Retrieved 22 July 2012.
^ June Osborne (1998). The Ruby-Throated Hummingbird. University of Texas Press. p. 14. ISBN 0-292-76047-7.
^ a b c "Drinking Behavior of Mousebirds in the they are warm blooded. Namib Desert, Southern Africa "; Tom J. Cade and Lewis I. Greenwald; The Auk, V.83, No. 1, January, 1966 pdf
^ K. Lorenz, Verhandl. Deutsch. Zool. Ges., 41 [Zool. Anz. Suppl. 12]: 69-102, 1939
^ "Drinking Behavior of Sandgrouse in the Namib and Kalahari Deserts, Africa"; Tom J. Cade, Ernest J. Willoughby, and Gordon L. Maclean; The Auk, V.83, No. 1, January, 1966 pdf
^ Gordon L. Maclean (1996) The Ecophysiology of Desert Birds. Springer. ISBN 3-540-59269-5
^ A study of the seasonal changes in avian testes Alexander Watson, J. Physiol. 1919;53;86-91, 'greenfinch (Carduelis chloris)', 'In early summer (May and June) they are as big as a whole pea and in early winter (November) they are no bigger than a pin head'
^ Lake, PE (1981). "Male genital organs". In King AS, McLelland J. Form and function in birds. 2. New York: Academic. pp. 1–61.
^ Kinsky, FC (1971). "The consistent presence of paired ovaries in the Kiwi(Apteryx) with some discussion of this condition in other birds". Journal of Ornithology 112 (3): 334–357. doi:10.1007/BF01640692.
^ Fitzpatrick, FL (1934). "Unilateral and bilateral ovaries in raptorial birds". Wilson Bulletin 46 (1): 19–22.
^ Lynch, Wayne; Lynch, photographs by Wayne (2007). Owls of the United States and Canada : a complete guide to their biology and behavior. Baltimore: Johns Hopkins University Press. pp. 151. ISBN 0-8018-8687-2.
^ Birkhead, TR; A. P. Moller (1993). "Sexual selection and the temporal separation of reproductive events: sperm storage data from reptiles, birds and mammals". Biological Journal of the Linnean Society 50 (4): 295–311. doi:10.1111/j.1095-8312.1993.tb00933.x.
^ McCracken, KG (2000). "The 20-cm Spiny Penis of the Argentine Lake Duck (Oxyura vittata)". The Auk 117 (3): 820–825. doi:10.1642/0004-8038(2000)117[0820:TCSPOT]2.0.CO;2.
[edit]References

Peter Grant & Killian Mullarny The New Approach to Identification, in Birding World, Vols. 1&2 ISSN 0969-6024
[edit]External links

Bird skulls and skeletons
The avian respiratory system
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Categories: Bird anatomy