WALRUS EYES!

Tavishi

The other day, my friend sent me a video of a walrus popping its eyes out of its sockets and asked me if it's supposed to be doing that.

TLDR; yes, they can.

Don't stop reading though because I have no hobbies other than talking about pinnipeds, and if y'all stop reading I'll be very sad.

Anyways, walruses have a couple cool adaptations that let them do that.

First off, y'all need priming in eyeball movement. There are seven extraocular eye muscles.

First, the levator palpebrae superioris. This muscle controls the upper eyelid's movement, and is innervated by the oculomotor nerve, which is cranial nerve III.

Also innervated by the oculomotor nerves are the superior rectus, inferior rectus, medial rectus, and inferior oblique muscles. If you look up, look down, look towards your nose, and move your eye from down to your nose, you'll use all of those muscles in that order.

Then, there is the superior oblique muscle, which rotates the eye medially, or towards your nose. This muscle is innervated by the trochlear nerve, or cranial nerve IV. Finally, the seventh extrinsic ocular muscle is the lateral rectus muscle, which moves the eye away from the nose and horizontally. This muscle is innervated by the abducens nerve, or cranial nerve VI.

One of the reasons why walruses can shoot their eyes out like that is because they lack an orbital roof. In humans, our eyes are caged in from the top. Walruse eyes, on the other hand, are supported by bone only from the bottom. The frontal bone forms no part of the orbital crest in walruses, but rather just stops before the eye.

Additionally, walruses rely almost entirely on monocular vision. Whereas humans constantly use both of their eyes, walruses are able to expand their visual field by just looking through one eye and moving it about- this is permitted by their extrinsic eye muscle adaptations.

Walruses generally use monocular vision more often than binocular vision.

While walruses have all the muscles as mentioned above, they also have a few extra that humans don't have. These muscles are the retractor bulbi externus and retractor bulbi internus, and they are innervated by the abducens nerve (CNVI).

This is responsible for pulling the eyeball inwards.

The actual telescoping of the eye in walruses is chalked up to its palpebral muscles (eyelid) muscles! Specifically, the levator palpebrae superioris.

This eyelid muscle is unusually thick and pronounced in walruses, which lets them do this:

More walrus facts because I like walruses and am too sleepy to make this post super coherent:

Walruses are the pinniped with the most vibrissae (whiskers). They have a lot of vibrissae on their face called mystacial vibrissae. The majority of a walrus diet is shellfish and other mollusks. They kinda just root around in the mud looking for clams, essentially. Their well developed mystacial vibrissae, however, allow them to have an advantage in looking for aforementioned clams. Whereas seal vibrissae are undulated, walrus vibrissae tend to be longer, thicker, and smooth.

They also sleep. a LOT. That's Ukiaq from the Alaska Sealife Centre.

Walruses are also the only species of pinniped with no fur. They're just skin and little bits of spiky hair.

Also, this is more of a funny note for anyone who's ever worked in an animal clinic, but wildlife veterinary med is a silly goofy gig sometimes. If you think it's hard to find a vein for a blood draw in dogs or cats, it's even harder in walruses. So much so, in fact, that an ultrasound is done prior to locate a draw site prior to Stealing blood.

ok bye !!!