I’m having Gorgons as a race in my story setting. They are not exclusively female, have the lower body of a serpent, and the classic snakes-for-hair element Gorgons had in Greek mythology. However, I’m not sure how the snakes that make up their hair would actually attach to their skulls. I know the snakes have their own hearts and lungs but no digestive organs, that they have their own brains which allow them to act autonomously to some extent, but that the Gorgons can also control them consciously when they want to, at least for the most part. But it’s the connection part that is giving me trouble. How does a snake spine attach to a humanoid skull?
Think of the tentacles of an octopus, and how they are connected to the head. No bones, yet they are mobile and rather autonomous.
As stated previously, the nervous system of an octopus can rival many vertebrates and unlike their molluscan relatives, octopuses' nervous systems are concentrated in their heads rather than being nerve knots or ganglia (Williams 2011). The nervous system is divided morphologically into three parts; the central brain, the optic lobe and the nervous system of the arms; the later two are located outside of the brain capsule and are fairly autonomous systems.
Same goes for the snake-hairs of your gorgon: the skull is covered with a mollusc-like tissue from which the tentacle/snakes/hair depart.
Warning: If you’re trypophobic (you don’t like clusters of holes) don’t think too hard about this answer.
What’s actually going on is that you have two species. The Gorgon is humanoid, bald, and has crater or bulb shaped indentations on their scalp/in their skull, with a lip over the edge. The Follicle Snake is a separate creature with powerful paralytic venom and a strong, coiled tail. The Follicle Snakes curl their tails into the indentation on their Gorgon’s head, seemingly becoming part of them.
This offers advantages to both species: The Gorgons get a weapon and the Follicle Snakes gain mobility, a constant heat source and a good, defended place to breed and grow. The Gorgon exerts control on their snake colony by tilting their head, flexing the muscles connected to their scalp (creating gruesome faces) and through training. The snakes in turn alert their gorgon to incoming threats by flexing (or just attacking immediately)
How did such a strange symbiosis come to be?
This is where it gets a bit squicky.
The Follicle Snakes are actually descended from a proto-snake that paralysed its prey before punching a hole in the skin, forcing its tail (hence the strength) under the skin, and laying a cluster of eggs to be incubated by the dying host before hatching and eating their way free. The Gorgons evolved a resistance to the paralytic venom but still occasionally were incapacitated and received a clutch of eggs. They found that by offering other foods to the newly hatching snakes, they could be enticed to not eat their host alive, and would instead remain just under the skin, periodically poking their tiny snake heads out to receive food before maturing and slithering into the wild, where they would hunt pests and other nuisance critters (like a horrifying reptilian cat).
Eventually this led to the domestication of the Follicle Snakes and almost ritualistic implantation of eggs in the scalp, where a pet snake would offer the most benefit and be the most visible to potential mates (who would be impressed by the obvious strength and vitality of a snake-bearing host). Fast forward a dozen generations and the mature snakes no longer leave the host, instead opting to stay cosied up on top of their heads as a venomous, writhing lapdog.
The ‘holes’ are really masses of scar tissue caused by repeated clutches of eggs being implanted, hatching and being nurtured by their now thoroughly social parents/Gorgons. Gorgons with a full head of snakes are seen as excellent breeding partners (with strong necks). Those with an unblemished scalp or few remaining scaly companions are poor or sickly. Good Follicle Snake breeds are docile, trainable or pretty, and can (with effort) be transferred from one owner to another or passed down family lines. The cycle of snake/gorgon interdependence is complete.
This does mean that your snakes could (hypothetically) act completely separately from their Gorgon of vice versa, but given the nature of the relationship it would probably be unlikely and require a lot of training the snakes.
Though if a Gorgon can train some of their friendly monstrous hairs to be mobile, stealthy snakes with a strong paralytic venom you also have an explanation for the whole ‘petrifying gaze’ myth...
Skulls with holes
There's two important things the snakes need. Blood and a sturdy connection. You could attach the snakes directly to the skull and have blood vessels move on the outside, but this would nullify a lot of the advantages of the skull. A hit on the head can easily destroy the quite large blood vessels and kill the Gorgon or in some cases the individual snake due to (internal) bleeding. Also the nerves would be quite vulnerable.
The blood vessels can most logically move through the brain, gaining protection of the skull. They don't need the protection of the dura mater, the protective layer around the brain. It can be fixed directly to the inside of the skull. Otherwise it can go straight through the brain, possibly using the voxels (fluid filled chambers for maintaining and further protecting the brain as it works) as much as possible to move to the skull and where it needs to be.
The skull itself doesn't need big holes per snake, as you can bundle the blood vessels and nerves (Gorgon needs to be able to control them) very well. The snake is then connected directly to the skull like normal muscles to bones. The hole in the skull isn't a bad thing, as the bundle of muscles and ligaments now protect the skull at that part very well.
To have a good degree of movement, the skeleton of the snake can attach to a bumb on the skull. The hole in the skull gets a raised bone, as if the spinal cord has (part of) a snake vertebrae fixed to the skull. This will further protect the skull and the hole, as well as aid connections for muscle and fiber, to allowing blood vessels and nerves to branch out safely.
The blood vessels might be connected by a form of placenta. This allows the separation of the hearts, blood pressures and whatnot, while still allowing for important nutrients and such to be transferred. It also allows a snake to die safely when cut, disease or old age. No bleeding out of the host. This would also allow new snakes to grow. Interestingly enough they could get some protection from the different immune systems, but these shouldn't be too different to work. Immune responses in normal pregnancy are already suppressed to prevent rejecting a baby. With snakes and Gorgons this could be much more difficult.
Mechanical, vascular, and neural connection
The snakes need three kinds of attachment. They need to be mechanically well anchored. This requires attachment points on the skull for the muscles and ideally for the spine as well. They need their blood vessels connected to the medusa's, because they do not have their own digestive systems---they get their nutrients via connected blood flow. But what most other answers neglect is the neural connection---if the medusa can override the snakes' brains and control them directly, then their spinal cords must be rooted into the medusa's brain.
These considerations yield the following: 1. The snake spines are connected to the skull in much the same way our spines connect to the pelvis. 2. The spinal cord and major spinal blood vessels pass through the skull and root into the brain and vascular system, respectively, on the inside of the skull. 3. The snake's muscles are attached to an annular enthesis on the skull.
Note that individual lungs and hearts in the snakes are not necessary at all. Instead the snake is all spine and muscle, which makes it stronger. It is essentially a limb, but with eyes and an autonomous brain, and a nasty venomous bite.