These are nice. Click through to empiggen.

I ripped them from Parker (1874), which appears to be a free download from JSTOR, here, and tweaked the colors just a bit.

If you are here for serious science, these guides to the abbreviations used in the plates will come in handy. I hacked the second one, below, to include the descriptions of the plates above, which are the last in the series, not the first.

EDIT: Nick Gardner pointed out that the copy of Parker (1874) at the Biodiversity Heritage Library is a slightly sharper scan, so if you’d prefer that version, it’s here.

Reference

Parker, W.K. 1874. On the structure and development of the skull in the pig (Sus scrofa). Philosophical Transactions of the Royal Society of London 164: 289-336.

 

Here’s how my pig skull turned out (prep post is here).

Verdict? I’m reasonably happy with it. As Mike wrote in the post that kicked off the “Things to Make and Do” series, “a pig skull is a serious piece of kit”. It’s big and substantial and it looks awesome sitting on the shelf. I learned a lot prepping it, and in particular I learned a couple of things that I will do differently next time:

  1. From now on I will cut the meat off first and grill only that, and not put the skull through the thermal stress of getting dry-cooked. Even with indirect heat, I think smoking the whole head did adversely affect the quality of the bone. The forehead and the rami of the mandibles in particular lost a little integrity. I painted the whole skull with a mix of 50% PVA (white glue, like Elmer’s) and 50% water, so it’s solid, but the surface bone is just slightly rough, I think because of degradation of the cortical bone.
  2. Before this I had only prepped small bones–small mammal and reptile skulls, vertebrae and long bones of domestic fowl, cannon bones and hooves of cattle. Stuff like that takes maybe an hour or two max to simmer, and to whiten, and that’s how I approached the pig skull. And it took forever, because I was doing short cycles, which meant doing a lot of them. I did a sheep skull this past holiday break, which I will post about soon, and I learned that the trick with bigger bones is just time. Simmer for 12 hours, not 2 hours, whiten for 2 or 3 nights, not just one. The sheep skull probably took more time from start to finish, but it was a lot less effort, because for much of that time it was just simmering, or soaking in dilute hydrogen peroxide.

With their deep lower jaws, pig skulls look rather lumpen in lateral view. But they look awesome in anterodorsal view, like dragon skulls. Here you can see that the prenasal bone is a little darker and less crisp than the other bones of the face. That’s because it was still ossifying from a big block of cartilage. I scraped off most of the cartilage, but not all, and what remained dried and hardened into an incredibly tough, translucent, slightly yellowish shell. 

I still have two pig heads on ice. I probably won’t do anything with either of them until I get some more time off, but I am looking forward to prepping another pig skull, in part to see how much better I can do the next time. But I’m still happy to have this one. To paraphrase another line from Mike’s old post, this is something that everyone ought to do.

Edit: here are some links about cooking pig heads and prepping skulls.

 

This is something I did over Thanksgiving break in 2019. I meant to blog about it sooner, but you know, 2020 and all. So here I am finally getting around to it. (Yes, I know the ruler in the above photo is the worst scale bar ever. I was, uh, making a point. Which you got. So go you!)

For reasons unknown to me, the strip of skin between the mid-snout and the ear on the right side of the head was already off when I took possession from the local butcher. But it did show the ear muscles to good advantage, as well as the parotid gland–the knobbly white thing between the eye and ear that looks like grits, or eggs, or white beans. You have a parotid gland in front of each of your ears, too (par-otid = “next to ear”), each with a duct that crosses the cheek to bring saliva into your mouth. If you push your tongue into the upper-lateral “corners” of your cheeks, you can feel the little papilla where the duct opens, and if you push against the papilla with your tongue you may feel a little saliva leak out. You also have paired submandibular and sublingual salivary glands, but those will have to wait for another day.

Here’s the head from the back, after I’d gotten the right ear off. The bluish-white hyaline cartilage over the occipital condyles is clearly visible about 2/3 of the way up from the bottom, with the faintly yellowish stump of the medulla oblongata in between, going up into the braincase. Tons of neck muscles are visible here, and maybe someday I or someone else will get around to labeling them in this photo–but it is not this day.

What was I doing here? Getting off the ears, and as much skin and subcutaneous fat as possible, in preparation for brining and smoking. I like this photo, the little piggy looks positively happy about having its skull prepped.

Right, into the bag with you then. I did the same brining and smoking routine that I did for my first smoked turkey back when–see this post for details.

And here we are about 15 hours later. Note how much the color of the meat has changed from the brining.

Time to extract the brain. I already showed a version of this photo in my post on the $1 brain-extractor (a.k.a. drain rooter, see this post), but it bears repeating: the brain is mostly lipids and if you cook the head with the brain still in it, the brain will turn into liquid fat and seep into the bones and you’ll spend the rest of your days trying to degrease the skull before you die, unloved and weeping, on a pile of rags. So no matter how you’re planning to cook the head, yoink the brain first.

Onto the grill, with a drip pan underneath, foil heat shields in place to keep the heat indirect, and foil-wrapped mesquite smoke bombs visible under the grill, right on top of the coals. This is about all I do with my grill anymore; smoking is really no more work than anything else and the results are pretty much to die for. YMMV.

Same shot an hour later and the smoking is coming along nicely. I ended up smoking this head for three hours, an hour and a half on each side. 

And into the roasting pan for a few minutes’ rest at the end of the cooking. And it was cooking, not just specimen prep–we ate this pig head in lieu of a turkey for Thanksgiving, and it was amazingly delicious. One thing to note in this photo is how the temporalis fascia has pulled away from the skull at the upper left, exposing some bare bone. This would be a problem later on.

Defleshing, both to get the edible meat off, and to get as much of the rest of the soft tissue off in preparation for simmering. In this anterior view, you can see that the right side of the animal’s forehead (viewer’s upper left) got exposed during the smoking process and the bone is stained brown. 

Even with the meat cooked all the way through, disarticulating the jaw took some doing, and then some follow-up meat removal. Check out the very round, almost hemispherical mandibular condyles, which fit up into the sockets of the temporomandibular joints. Birds and other reptiles mostly do it the opposite way, with rounded quadrates on the cranium that fit into articular sockets on the lower jaw.

Ready for simmering. Pro tip: if you need a really big metal pot in which to simmer skulls or other large osteological specimens, but you don’t want to go bankrupt, look for a tamale-steaming pot. They’re comparatively thin-walled and lightweight, but still plenty sturdy for just about any application you are likely to think of. 

Our kitty, Moe, helped with the clean-up of the roasting pan.

The first simmer. At this remove, I don’t remember how many rounds of simmering I did, but it was at least two, maybe three.

Post-simmer, I put the skull into a sink-full of warm, soapy water for a defleshing. Notable bits you can see on the right side of the photo are the ridged surface of the palate (about 7:00 on the plate), the long straight cartilage of the nasal septum (going vertically up the right side of the plate), and the incisors at the extreme upper right, sitting on the edge of the sink. Most of the incisors fell out during the wash, which was fine, because most of them were horribly stained from the smoking process and would require a lot of scrubbing and bleaching to get back to a nice and natural-looking white.

The condition after the first simmer. You can see that the supraorbital foramina, on the forehead between the eyes, still have goop in them. This was true of pretty much all of the nerve and blood vessel passages. It took a lot of time, some ingenuity, bamboo barbeque skewers, and running water this way and that to flush out all of that crud. And the bones are still weird colors at this stage, pre-whitening, especially the groady dark patches on the forehead. It wasn’t the areas of bone that were directly exposed to smoke that were the problem, it was the areas just adjacent where the periosteum cooked against the bone.

Same stage, left lateral view. Note the empty sockets for the incisors, and the infraorbital foramen (above the upper teeth and about a third of the way between eye socket and the nose), which on this side is divided in two by a strut of bone. There’s another gross dark patch on the back of the zygomatic arch. All of those took pretty aggressive scrubbing to remove.

Back into the pot for another simmer. The perforated plate at the bottom sits on a lip of metal about three inches above the bottom of the pot so you can steam tamales with this thing. I used it to keep the bones off the bottom of the pot so they’d have no chance of getting scorched.

Here’s a significant jump forward in time. By this point I’d degreased and whitened the skull by soaking it in dilute hydrogen peroxide (I use the cheap stuff from the dollar store down the street, and it works fine), applied glue to several of the skull sutures that were threatening to come apart, and epoxied the prenasal bone back into position between the nasal bones above and the premaxillary bones below. The prenasal bone is a pretty cool structure, you can see it in other views (including a cross-section!) in this post. I also glued the incisors back in at this stage.

Believe it or not, this was the largest skull I had ever prepped myself–the largest osteological preparation of any kind, in fact–and it was a lot more work than I anticipated. But the effort was worth it, and now I have a really cool pig skull on my bookcase. I’ll show the finished skull in a follow-up post (no, really, I will!). EDIT: And I did! 

For other posts on pig skulls, see:

From Will’s Skull Page, here.

Here’s a skull of a wild boar. Note the loooong face, practically a straight line from the tip of the snout to the top of the back of the head.

We shall now proceed through a series of pig skulls with increasingly steep foreheads.

From the UCL Museums and Collections blog, here.

Some domestic pigs have a longish snout and nearly straight forehead, like their wild forebears. (Or foreboars, if you will.)

A cast skull from Carolina, available here.

But it seems–from a quick, unscientific, and in-no-way-standardized image search–that the vast majority of domestic pigs have at minimum a more steeply-inclined forehead.

This one was auctioned in New Zealand, at this site.

Foreheadization is becoming undeniable.

From skullbase.info, here.

Is this one any more pronounced than the one before? I’m not sure, and so far I’m too lazy to try superimposing the skulls. But they don’t even look like the same kind of animal as the wild boar shown at top.

From theweirdandwonderful.com, now apparently only available on Pinterest, here.

In my explorations so far, this appears to the ne plus ultra of short-faced, high-forehead domestic pigs, excluding truly pathological cases. The line from the inflection point of the forehead to the occiput is twice the length of the snout!

From theweirdandwonderful.com, now apparently only available on Pinterest, here.

Oddly enough, the high forehead in domestic pigs is not always associated with a super-short snout, as this skull demonstrates.

This figure from Owen et al. (2014) sums up the shape differences between domestic (left) and wild (right) Sus scrofa.

Okay, so domestic pigs have shorter snouts and steeper foreheads than wild pigs of the same species. But y tho? It seems to be part of the “domestication syndrome” present in many domesticated animals, which includes a shortened snout, smaller teeth, piebald coloration, floppy ears, a curly tail, and a host of other morphological and behavioral traits. Interestingly, pigs seem to show more aspects of domestication syndrome than any other domestic animals other than dogs, as shown in the figure below, from Sanchez-Villagra et al. (2016).

Okay, so domestication, but how? It’s not like the Domestication Fairy comes in the night and steals half your snout.

Wilkins et al. (2014: fig. 1)

The various morphological changes that go along with domestication syndrome seemed disconnected until 2014, when Wilkins et al. proposed a pretty nifty hypothesis, which goes like this:

  • Probably the most crucial aspect of domestication is selection for tameness, which is really selection for reduced adrenal gland and sympathetic nervous system activity, so the animals aren’t freaking out all the time.
  • The adrenal glands and sympathetic ganglia are derived from embryonic neural crest, which also influences the growth of the teeth, brain, skull, vertebral column, and ear cartilages, and the distribution of melanocytes in the skin and coat.
  • Selection for increased tameness (= reduced freaking out) is really selection for reduced neural crest activity in early development, and the smaller teeth, shorter snout, floppy ears, curly tail, patchy coloration, and so on, are unselected developmental consequences of reduced neural crest activity.

Wilkins et al. (2014: fig. 2)

So far, so good. The neural crest hypothesis seems to have genuine explanatory power, in that it lassos a disparate set of phenomena and provides a single, logical cause. Of course not everyone is convinced, and the neural crest hypothesis could be true without ruling out other complementary mechanisms and confounding effects. Along those lines, Sanchez-Villagra et al. (2016) is worth a read. It’s free at the link below, as is Wilkins et al. (2014).

The neural crest hypothesis might explain why domestic pigs have shorter snouts than their wild relatives, but I think there must be some other factors in play to explain pig foreheads. Which is fine, domestic dogs have a staggering variety of skull shapes that reflect thousands of years of strong artificial selection, and probably a healthy dose of unintended consequences and other knock-on effects. Given that pigs have been domesticated for a long time, were probably domesticated many times in many places, have had frequent infusions of wild-type genes (from possibly genetically disparate wild populations), and have been canalized into different breeds, it might actually be weirder if they all looked like short-snouted wild boars. All of which is a long way of saying that I’m not surprised that domestic pigs don’t all fall on some morphogenetic monocline from wild boars, but I’m still curious about how they got their foreheads.

I actually started writing this post before the very interesting discussion of pig domestication flared up in the comments on Mike’s pig skull post. Mike’s two skulls nicely illustrate the difference between forehead-less and, er, forehead-ful conditions, and the comment thread touched on a lot of related issues and is worth a read. In particular, I’d like to note again that domestic pig skulls are not notably paedomorphic with respect to wild boars, other than having short snouts–they’re on a different morphogenetic trajectory (Evin et al. 2016).

For a nice comparison of domestic pig and wild boar skulls, see Marcus Bühler’s post at Bestiarium, here.

UPDATE just a few days later: for a skeptical look at the very existence of domestication syndrome, see the new Lord et al. (2019) paper, “The history of farm foxes undermines the animal domestication syndrome”, freely available here.

References

Long-term readers will remember that way back in the pre-history of this blog, I wrote about my experience de-fleshing a pig head, which because the very first part in our ongoing series Things to Make and Do. In a subsequent post with a sheep-skull multiview, I included the multiview of that pig skull, too. Here it is:

Mike’s first pig skull, cranium only. Top row: dorsal view, anterior to right; middle row, from left to right: posterior, right lateral and anterior views; bottom row: ventral view, anterior to right.

As I noted in that sheep-skull post, I no longer own that skull: I donated it to be the first prize for the quiz in the very first TetZooCon, and it was won by Kelvin Britton.

But around the same time, our church hosted a barbecue even in which an entire pig was slow-roasted, and at the end of it I took the head home and prepped the skull out of it. The bone was much more fragile for having been roasted instead of simmered, and was in some danger of crumbling apart, but I stablised it with diluted PVA and it holds together OK.

Here it is:

Mike’s second pig skull, cranium and mandible in articulation. Top row: dorsal view, anterior to right; middle row, from left to right: posterior, left lateral (reversed) and anterior views; bottom row: ventral view, anterior to right.

Even allowing that the new skull was photographed with the mandible in place, the difference between the two is shocking. In particular, check out the dorsal views: the zygomatic arches of the first pig protrude way further laterally, and are much more robust than those of the second pig, and the whole shape of the skull roof is different.

I’m not sure what to make of this. I assume what we’re seeing here is variation of different breeds within the single domesticated species Sus domesticus, analogous to the way bulldog and greyhound skulls differer dramatically despite both being breeds of Canis familiaris. There are a lot of pig breeds out there, so perhaps it’s not too surprising. On the other hand, while the different dogs were bred for different purposes, I’d have thought all the pig were bred for the same purpose: to put on weight and provide meat. So I don’t know why such different skulls would have been selected for.

Well, it’s time. Ten years and almost 5 months after Mike kicked off our “Things to Make and Do” section with his post on cleaning a pig skull, I am finally getting around to prepping a pig skull of my own. There will be a complete play-by-play coming, but for now I want to focus on what is usually the least-pleasant step in prepping a skull: extracting the brain. Aside from the relatively small and often tortuous passages for the cranial nerves, the braincase is a cul-de-sac, with a big glob of tissue (the brain and associated meninges and vessels) only accessible through a relatively small hole at the back of the head (the foramen magnum). Virtually every tutorial and how-to on prepping skulls has some section where the author advises you to basically swirl something around in there, get stuff out the best you can, and prepare to deal with a lot of nastiness along the way. So I had my antennae out for anything that might help, and in the local dollar store I ran across the beauty shown above.

I figured drain rooter = brain rooter, and I was only risking a buck, so I picked one up. It worked a trick: by putting the pig’s snout down the drain, running hot water into the foramen magnum to continually flush out the loose bits, and vigorously exploring the cranial cavity with the brain rooter, I was able to get the whole brain out in about 10 minutes. To be clear, all the tissue came out the foramen magnum; there would be no way to get it to come out the nose without breaking the ethmoid bone and destroying the nasal turbinates. I only put the head snout-down for ease of access. I had a great deal of control, and I could tell pretty well which areas were getting emptied out and which still needed work. All I missed was a small glob of meninges and dural venous sinuses, which came out easily after the first simmer.

Some specific advantages of the drain rooter as a brain extractor:

  • backward-pointing teeth to hook out the tissue
  • flexible plastic so you can go pretty hard with it without damaging the bone
  • super long so you’re not going to find a job too big for it, OR you can cut it to length
  • still works for unclogging drains
  • dishwasher safe
  • dirt cheap

Go have fun.

UPDATE: Turns out pigs have an insane amount of cartilage and mucosa in their nasal cavities, and the brain rooter is pretty good at getting that stuff out, too.

Here’s a frozen pig head being hemisected with a band saw.

The head in question, and the other bits we’ll get to later on in this post, both came from Jessie Atterholt’s Thanksgiving pig. As soon as Jessie knew she was cooking a pig for Thanksgiving, she had a plan for the head and the feet: cut ’em in half, skeletonize one half (like Mike did with his pig head), and plastinate the other. Jessie has her own plastination setup and you can see some of her work in her Instagram feed, here.

Here’s the freshly hemisected head. At one time or another, about four of us were involved in checking the alignment of the cut, with the intention of just missing the nasal septum (it can be easier to see some of the internal nasal anatomy if the septum’s all on one side). But we were all wrong–not only did the saw hit the nasal septum dead on, it hemisected the septum itself. Which I guess is the next-best possible outcome. The septum is the big expanse of white cartilage behind the nose and in front of the brain. You have one, too–it separates your left and right nasal cavities–but yours is a lot thinner.

Here’s the left half washed off and cleaned up a bit.

I was completely entranced by the little blood vessels inside the nasal septum, seen here as tiny traceries of red inside the blue-white cartilage. Also notice the frontal sinus above the septum and in front of the brain.

Here’s the right half in a postero-medial oblique view. Shown well here are the first two cervical vertebrae, plus part of the third, and the intervertebral joints. This was a young pig and the remains of growth plates are still visible between the different ossification centers of the vertebrae. If I get inspired (= if I get time) I might do a whole post on that.

It wasn’t my pig or my show, but Jessie made me a gift of two pig feet, and I got a little time on the saw. Here I’m using a plastic tool to push one of the pig’s hind feet through the saw.

We had been dithering over how best to prep the feet but the lure of the band saw proved irresistable: we hemisected all four. We’re planning to do half skeletonized/half plastinated preps for all of them, a forefoot and a hindfoot set for each of us.

Jessie and I were joined by two other WesternU anatomists, Thierra Nalley and Jeremiah Scott. Here Thierra is explaining to Jeremiah, who works on primate dentition and diet, that mammals have more parts than just teeth.

That’s a good segue to this video I shot, in which Thierra gives a quick tour of the hemisected pig head. All four of us have just come off of teaching human head and neck anatomy, so it was cool to see in another mammal the same structures we’ve just been dissecting in humans.

From 1:40 to 1:55 in the video Thierra and I are discussing the prenasal bone, something pigs have that we don’t. It’s the separate bone at the end of the snout in this mounted skeleton:

Darren discusses and illustrates the prenasal bone in this Tetrapod Zoology post.

Parting shots: many thanks to Ken Noriega and Tony Marino of WesternU’s College of Veterinary Medicine for their guidance, assistance, and expertise. Jessie covered this dissection as an Instagram story, here–I believe you have to be signed in to see it. Update: Jessie added a regular stream post, with lots of features labeled, here. I’ll probably have more to say about this pig and its bits in the future. Stay tuned!

For more hemisected heads and skulls, see: