The Amphisboenoida

These lizards have completely snake-like bodies; one genus of the group (Chirotes) has a pair of small pectoral members, but the rest are apodal. The integument of the body is not scaly, but its surface is divided into small rectangular areas arranged in transverse rows. The tail is exceedingly short, so that the vent is close to the end of the body.

The numerous procoelous vertebrae have less elliptical articular faces than those of the typical Lacertilia. There is no sacrum, and all the precaudal vertebrae, except the one or two of the most anterior, have ribs. The representatives of the chevron-bones in the tail are firmly united with the centra of the vertebrae. The vertebrae have no zygantrum nor zygosphene. Amphisbaena has no sternum. Chirotes has a sternum, but it is not united with the ribs.

The skull, unlike that of Lacertilia in general, develops no interorbital septum. In this respect, and in the complete closure of its anterolateral walls by bone, it resembles the Ophidian cranium. There is no columella. Post-frontals are absent, and the squamosal is very small. The quadrate bone is small, and inclined not only downward, but forward, in a manner unknown in other Lacertilia. The two rami of the mandible are firmly united by suture.

In Amphisbaena the premaxillae bear two rows of teeth, one behind the other, and one tooth lies upon the symphysis of the premaxillae.