An epiglottis may be present in vestigial form, but there is often fusion of the cartilages here to form a glottal tube. When the mouth is closed, the internal nostrils are positioned directly above the entrance to the trachea. Snakes, like all reptiles other than crocodilians, do not have a hard palate. The nostrils are paired and open into the roof of the mouth. That is, they will shed their tail if roughly handled or caught by a predator. It is by alternately contracting and relaxing these segmental muscles that the snake can propel itself across the ground, the caudal edge of each ventral scute providing friction.Ī very few species of snake, such as the glass snake, exhibit autotomy. This muscle is segmental and supplied by intervertebral nerves.

The ventral scales, known as scutes or gastropeges, overlie the muscular casing of the snake’s torso. The site for this is one third the distance from the vent to the tail tip on the ventral aspect. This vein can be used for venipuncture both for sampling and for intravenous injections. Instead they have paired, ventral, haemal processes between which the coccygeal artery and vein run. The coccygeal vertebrae (those caudal to the vent) are the only vertebrae with no ribs attached. The skull articulates with the atlas vertebra via a simple joint containing only one occipital condyle, rather than the mammalian two. The maxilla also hinges only loosely with the rostral aspect of the cranium, so allowing the nose of the snake to be raised, increasing the oral aperture. Instead it possesses a quadrate bone, which articulates between a mandible and the skull and allows the mandibles to be moved rostrally and laterally, ‘dislocating’. In addition, the snake has no temporomandibular joint. In all snakes, the two halves of lower jaw are loosely held together rostrally and the mandibular symphysis can separate. The anatomy of the snake’s head has a number of adaptations that allow it to swallow large prey. It is worth mentioning that owners (other than zoos) of poisonous species of snake, such as pit vipers and rattlesnakes, must be licensed and registered in the United Kingdom under the conditions of the Dangerous Wild Animals Act of 1976.įigure 17.1 Intraoral view of a young Burmese python showing the four upper and two lower rows of teeth, as well as the glottal tube and tracheal entrance, rostral to which is the tongue sheath. All teeth are replaced as they are lost, including fang teeth in poisonous species. Rattlesnakes, for example, have hinged, rostrally situated fangs which swing forward as they strike.

Some of the more poisonous species have specialist adaptations. The more commonly seen non-poisonous species such as the colubrid family (containing the kingsnakes and rat snakes) and the boid family, have simple, caudally curved, peg-like teeth. The teeth vary somewhat between the genera. The mandible has the more normal two rows of teeth ( Figure 17.1). The maxilla has 4 rows of teeth, two on either side. The snake skull possesses a small cranial cavity containing the brain and a large nasal cavity. These can possess vestigial pelvic remnants, having claw-like spurs either side of the vent representing the hind limbs. There are some remnants of limbs in one or two of the older evolutionary species of snake such as the boid family (pythons and boa constrictors). This distinguishes them from species such as the slow worm, which is actually a lizard with vestigial limbs. Instead it has a coelomic, or common, body cavity.Īll true snakes have no limbs. Like the bird, the snake has no diaphragm, so no separate thorax and abdomen. Scincomorpha (skinks, whiptail lizards and European Lacertid lizards)Ĭontains the order Crocodylia which contains the following familiesĪlligatoridae (the alligators and caimans) Suborder Scleroglossa which itself is then split into the following infraordersĪnguimorpha (Monitor lizards, Heloderma lizards, slow worms etc.)

Suborder Iguania (containing the Agamids, Iguanids, Chameleons and New world lizards) More recently the order Squamata has been divided into the: Suborder Serpentes (i.e., the snakes) suborder Lacertilia (i.e., the lizards) suborder Amphisbaenia (the worm-lizards)

Common boa constrictor anatomy