This study was undertaken to examine the relation between the possession of the so-called pit organs, which are sensitive infrared receptors innervated by the trigeminal nerve, and the sensory trigeminal nuclei. The sensory trigeminal system of Python reticulatus was investigated by means of myelin and Nissl staining techniques.

It appears from the study that the sensory trigeminal system consists of two separate components. One of these resembles the sensory trigeminal system, known of other vertebrates, and is referred to as the common sensory trigeminal system. It comprises a short ascending part to the principal sensory trigeminal nucleus and a longer descending part to the nucleus of the descending trigeminal tract and upper cervical segments. The subdivision of the trigeminal system, as proposed by Olszewski ('50) for mammals, could be applied to the common sensory trigeminal system of the python.

The second component is situated laterally to the common descending system. It is composed of descending fibres which terminate in a huge, separate nucleus. This is called the nucleus of the lateral descending trigeminal tract. This component was initially recognized in snakes possessing infrared receptors, but seems not to be restricted to these animals.