Avian Anatomy

Our last anatomy lab was on avian anatomy, so we dissected chickens. Here is an account of some of the things I thought were interesting.

You'd be surprised how few feathers they actually have. When they're alive they're all poofy, but for dissecting they had us dip them in soapy water so that feathers wouldn't be floating everywhere all lab (I'm serious), and you can really see that there's not as many as you'd think.

Birds have a super massive keel on their bellies, part of their sternum. Imagine your sternum down your chest, but with a big fin. Most of  their bones are the same as mammals, but lots of things are fused. Most of their vertebral column is fused, which gives them stability and allows them to have less back muscles, which makes them lighter. The wishbone is their clavicle. Another interesting bony structure is the bone in their tongue--they don't have tongue muscles; the movement is conducted through their tongue bone.

Birds have a different voice organ than mammals, called the syrinx (we use our larynx). Something interesting I read is that songbirds and such that make a lot of complex sounds don't necessarily have a more developed syrinx or associated muscles.

Their brains are tiny, which I'm sure you already knew. What you might have not known is that their eyes are huge, way bigger than they appear because they aren't a sphere. Each eye is about the same size as the brain. Also their skull is kind of thick too, so if you're just looking at a bird and try to picture the size of their brain in their head, it's actually way, way smaller than you'd think just by doing that. They can have pretty super vision, but I don't think their brains do a whole lot else for them.

Birds don't have a diaphragm: they depend on moving their body wall to draw air into their lungs. So if you hold a bird so it can't move it's chest, it won't be able to breathe. They also have a pretty cool system, where air gets drawn into these air sacs and  then into the lungs and then into other air sacs before being exhaled, so that the air going into the lungs is always fresh. Being so efficient is why they can fly very high, where the oxygen is low.

Their gastrointestinal, urinary, and reproductive tracts all open into this one pouch and exit the bird through the same hole. They sort of have two stomachs--one that's glandular, and one that's super muscular (the gizzard). That's kind of neat because it actually utilises ingested stones to help grind up food. Their testicles don't descend (they stay inside the abdomen), and sometimes the only way to sex a bird might be using internal imaging. They also don't have a bladder.

If you look at the ovary, you can see a bunch of big red follicles, like the ones that will be tomorrow's egg and the next day's. They're super huge! And if you break one by accident, you get yolk everywhere. In our bird, it had actually had a ruptured part of its reproductive tract, so there was an egg that hadn't got its shell yet, and it was just hanging out inside the bird. It looked just like it would have if you'd cracked one and dropped it in.

The nerve that innervates their hind limbs passes over the kidney, so if they have kidney disease or a tumour or something, it can actually present as lameness.

Perching is a passive thing. When they bend their knees, it tenses the tendons that flex their digits, causing them to grip. It takes no energy for them to sit there gripping a branch, and if you want to un-perch them you have to straighten their legs.

Some birds, such as owls, have asymmetric ears so they can localise sound better. Also, birds have magnetite in their beak and neck muscles, which is an iron rich crystal that responds to the Earth's magnetic field. This gives them both directional and geographical location information.

Those are all the cool facts about birds I can think of for now, I hope you learned something.