Out of Africa
The digestive system of snakes
Given their tube-like body shape, snakes have had to undergo some pretty radical adaptions to their anatomy in order for them to survive and thrive in this state. Unsurprisingly, their digestive system is no exception to this rule, as Paul Donovan explains.
Photo courtesy Tarakanbix/
www.shutterstock.com If there’s one thing snakes in general are known for, it is their ability to overpower and eat prey significantly larger than their anatomical girth. All species of snake basically feed in the same way, with prey being swallowed whole rather than being chewed up, in spite of the presence of a formidable battery of teeth in their mouth. These serve to capture and anchor prey however, so that it can be overpowered, in the absence of limbs.
An olive python that has just caught and largely swallowed a rock wallaby, distending its body quite considerably.
Photo courtesy Ken Griffiths/
www.shutterstock.com Its morphology
There are some other interesting ways in which the digestive system of snakes differs from that of other animals too. It nevertheless consists of a number of similar distinct sections. These are the oral cavity (mouth), oesophagus (gullet), stomach, small intestines, caecum (in a number of species), colon (large intestine) and cloaca.
One area where specialisation is very apparent is in the mouth. Not only in the layout of teeth, but in terms of their structure and the formation of the oral glands, with specific venom glands (where present) which allow prey to be immobilised. The anatomical arrangement here facilitates the swallowing of prey, and enables the digestive process to get underway.
Expandable jaws
In order to allow for relatively large prey to be swallowed easily, and to avoid any risk of choking the snake, the jaws have had to become expandable. They articulate to accommodate prey which can be up to five times bigger in some cases than the actual girth of snake’s head or body.
The ability to swallow large prey is dependent upon several factors; notably the elasticity of the ligaments which connect the bones of the lower jaw; the mobility of the upper jaws, which are not fused to the skull as they are in mammals, and the shape of the teeth. The upper and lower jaws essentially consist of four longitudinal parts which can work independently from one another. Not only can the lower jaw distend downwards, but also sideways. This is possible thanks to ligaments which ‘attach’ the bones together at the front.