The tritocerebrum is linked to subesophageal ganglion by circumesophageal connectives and to the frontal ganglion by frontal commisure. This part of the brain has efferent and afferent connectives to certain mouthparts. The subesophageal ganglion is the first ganglion in the ventral nerve cord. This ganglion has motor and sensory connections to salivary glands, mouthparts, and neck. Most insects have three thoracic ganglia, each with connectives to muscles and sensilla.
Abdominal ganglia have connections to muscles, though usually fewer than thoracic ganglia.
Numbers of ganglia vary among groups of insects. The thoracic and abdominal ganglia are fused into a single compound ganglion in houseflies. This is an example of extreme fusion. The least fusion is shown in a thysanuran. The last abdominal ganglion is always a compound structure, derived from the ganglia of the last four segments.