Snakes: A Look Inside

Snakes are relatively long and thin. So where do all their organs go? In order to understand a snake's insides, we must first understand its skeletal structure.

Simple Skeleton

With the exception of the skull, a snake's skeletal structure is fairly simple. The trunk and tail of a snake consist of 200 to over 400 vertebrae. Most trunk vertebrae have two ribs attached. Ribless vertebrae include 5 to 15 in the trunk and all of the vertebrae in the tail. The number of vertebrae in the tail is less than 20% of the total number of vertebrae.

Often, the number and size of a snake's vertebrae correlates to the snake's method of subduing its prey and speed of locomotion. Snakes that constrict their prey need to be able to make tight coils with their bodies. These snakes generally have a large number of small vertebrae with muscles that link only a few vertebrae. This makes the snake slower. Pythons and boas tend to be slow-moving and constrict their prey.

Snakes that do not require extreme flexibility to take down their prey have larger vertebrae and muscles linking many vertebrae. This allows the snake to travel more quickly. Not surprisingly, the fastest snakes in the world are also venomous, relieving them of the need to constrict.

The Amazing Flexible Skull

Cranial kinesis, the presence of moveable joints within the cranium, is present in many vertebrates. (Mammals are unique among tetrapods, vertebrate animals with four appendages, because we have no members that exhibit any degree of cranial kinesis. This is why the notion of a flexible skull seems so strange to many people). Snakes have the highest degree of cranial kinesis among tetrapods, and are included in this category because they evolved into their current legless forms.

The snake skull contains many joints that provide a wider gape and greater jaw flexibility. These joints also allow the snake skull to move a certain degree. Mandibular liberation is the condition in which the mandibles, the bones that comprise the lower jaw, are not rigidly connected. Therefore, snakes have the ability to move the two parts of the lower jaw separately. These modifications allow a snake to squeeze into tight places, and to swallow prey much larger than itself in diameter.

A Lonely Lung

The evolution of a long, tubular body inevitably has consequences related to organ shape and placement. One major repercussion is that in most species, only the right lung is functional. The left lung is much smaller and sometimes completely absent.

Organs all in a Row

Most of the other organs have been elongated to accommodate the snake's body shape. Their positions have also been slightly altered. For example, paired organs like the kidneys are located one in front of the other rather than on either side of the body. A snake's heart, unlike the human heart, is not held in a fixed position in the body. With snakes, there is room for the heart to shift from side to side. This wiggle room prevents the heart from being damaged when the snake swallows large prey items.

Snake Brains

The brain of a snake is similar to that of a bird; however, the enlarged cerebral hemisphere is missing. This is the portion of the brain that facilitates learning. Although this may mean that snakes aren't especially intelligent animals, they do have the ability to learn associations between certain chemical or visual cues and certain events or individuals.

For example, one of the first associations a snake learns is the smell, size, and movement of its prey. If a snake can smell its prey, it will try to follow the smell and looking for prey-like movement (such as the fast breathing and scurrying of a mouse). In captivity, if handled enough, a snake will learn the smell that is associated with its handler. These animals learn what their shelters look like and can remember where water is, where their hiding place is, and where their neighbors live. If there is enough traffic through the room, snakes will also become accustomed to the movement of people walking by.

Next Time

A snake's sense of smell is so well-developed that it can tell the difference between one individual and another. Snakes can also smell their prey long before they ever see it.

So what about a snake's other senses? That's a discussion for next time. See you then!

Picture Sources

wikipedia.org
sensationalserpents.com

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