Creature Features: Snakes and Serpents

In honour of this being the Year of the Snake, I thought we could talk about snakes. They are a common phobia, and culturally they have had quite an impact on human society. From the Garden of Eden to Cleopatra’s death, snakes are often thought of as evil or dangerous. Yet other people love them and they are a common exotic pet.

A warning for those with ophidiophobia, fear of snakes, this series of articles will contain photographs of snakes occasionally. So feel free to skip these ones if you like. The anatomical diagrams will hopefully be less of a problem. That said, let’s get into it. We’ll start with some snake anatomy and physiology – discussing some of the unique features of serpents. Then we’ll look at the real life dangers of snakes, and finally a discussion of the cultural impact these creatures have had.

I have a video going through these details here, if you’d prefer that format.

Basic Snake Anatomy

Snakes are limbless reptiles, with long thin bodies and protective scales. They lack eyelids but generally have good vision. Their diet is carnivorous and they strike with venom or constrict their prey, before swallowing it whole. Most snakes lay eggs, but there are a few that deliver live young.

Like all reptiles, they are ectothermic. You might know this as ‘cold-blooded’ but it means that they control their body temperature by using their environment instead of generating body heat internally. So they bask in the sun to increase their temperature and hide in the shade or burrow to cool down.

Internal Organs of Snakes

Here’s a quick overview of their organ layout. They only have one full lung, the right lung. The left lung is small and not involved in oxygen exchange, but may have an immune function. Air sacs extend from the functional lung, storing air and allowing snakes to hold their breath for a long time. The heart has three chambers: a single ventricle and two atria. It is located near the end of the first third of the body length. There is no diaphragm to separate the chest and abdomen.

The rest of the organs are as expected: a liver, two kidneys, a spleen, a gallbladder, stomach and intestines and reproductive organs. A male snake has a pair of testes and a pair of hemipenes (yes, they have two penises essentially) that lie within the tail when not in use. Female snakes instead have ovaries and an oviduct (kind of like a uterus.) Eggs are formed and held in the oviduct until they are ready to be laid, or hatch before the live young are born.

1. oesophagus
2. trachea
3. tracheal lungs
4. rudimentary left lung
5. right lung
6. heart
7. liver
8. stomach
9. air sac
10. gallbladder
11. pancreas
12. spleen
13. intestine
14. testicles
15. Kidneys

Snake Skeleton Anatomy

Snakes have no limbs and there is nothing left of the pectoral girdle: shoulders, collar bones etc. Boas and pythons do have vestigial pelvic bones and claws, but most of the more recently evolved species don’t have this at all.

The body skeleton is made up of vertebrae and ribs: from 175 to 400 vertebrae can be present. Almost all of them have a pair of attached ribs, except the first couple attached to the skull, and the caudal vertebrae that make up the tail of the snake. The division between body and tail can be seen externally when the belly scales change from one single scale to paired scales – just beyond the vent (the genital opening.)

Snake Skull and Jaws

The snake’s skull is extremely complex. The jaw has an extra bone called the quadrate bone and extra joints that allow for the snake to open its mouth wide enough to swallow prey larger than its head. Each side of the mandible, the lower jaw, can move independently as well.

There is significant variation in anatomical structure between different species. The details of this are beyond the scope of this article but if you are interested you can find an in-depth explanation here: https://en.wikipedia.org/wiki/Snake_skeleton#Joints_of_the_snake_skull

Lateral view of the skull of a Burmese python, with visible kinetic joints labeled. Red = highly mobile, green = slightly mobile, blue = immobile.

• Red A: the joint between the mandible and quadrate. It is analogous to the joint in mammalian jaws.

• Red B: the joint between the quadrate and the supratemporal. It is highly mobile in most directions, allowing a wider gape (i.e., the snake can open its mouth wider) and greater jaw flexibility.
• Red C: the joint between the prefrontal and maxilla. It allows the maxilla to pivot in the plane of the photograph, and while it does not increase gape, it does facilitate the complex action by which the snake draws prey into its mouth.
• Green A: the joint between the frontal bone and nasal bone. It allows the nose to upturn slightly, increasing gape and assisting in swallowing.
• Green B: allows the lower jaws to bow outwards, further increasing the gape.
• Blue: the joint between the supratemporal and parietal. Immobile, except for Dasypeltis.

Snake Teeth

The teeth are curved and point backwards towards the throat to allow for the snake to slowly ingest the whole prey. Venomous snakes have specialised teeth that can deliver venom after a bite such as the ‘fangs’ with grooves to deliver the poison.

Snakes can strike fast, curling their bodies and arching forward to bite and deliver venom or grab hold of the prey so they can constrict it and kill it. The above link has more details on the different kinds of dentition seen in snake species.

Thanks for reading this brief introduction to snake anatomy Next week we’ll discuss a bit more about snake physiology and some of their unique features, so I hope you’ll come back for that. See you soon!

• TikTok
• Instagram
• Facebook
• YouTube
• Threads
• Bluesky
• YouTube