The anterior end of body always shows some "cephalization."
Regard is had to the existence of anterior rights or duties.
First two premolars with compressed and sharp-pointed crowns, and slightly developed anterior and posterior accessory basal cusps.
The molar teeth are six in number on each side, increasing in size from before backwards, and, as in the elephants, with a horizontal succession, the anterior teeth being lost before the full development of the posterior ones, which gradually move forward, taking the place of those that are destroyed by wear.
These two vessels in the Oligochaeta are united in the anterior region of the body by a smaller or greater number of branches which surround the oesophagus and are, some of them at least, contractile and in that case wider than the rest.