In the tail region of other forms each vertebra consists of an anterior centrum bearing the neural arch, and a posterior intercentrum[61] bearing chevron bones. Vertebrae of this type are called _embolomerous_. Haemal arches similar to the neural arches are often found as in Urodela. The transverse processes are sometimes well developed and are divided into tubercular and capitular portions. In Gymnophiona the vertebrae are biconcave and are very numerous, they sometimes number about two hundred and thirty. Only quite the last few are ribless and so can be regarded as post-thoracic vertebrae. The first vertebra has nothing of the nature of an odontoid process. In Anura the number of vertebrae is very greatly reduced, only nine and the urostyle being present. Of these, eight are presacral and one sacral. The urostyle is post-sacral and corresponds to three or more modified vertebrae. The first vertebra is without transverse processes, the remaining presacral vertebrae have the transverse processes fairly large, while the sacral vertebra has them very large, forming in some genera widely expanded plates. The urostyle is a long cylindrical rod which articulates with the sacrum generally by two facets. Ankylosed to its anterior end are the remains of two neural arches. In Anura remains of the notochord are found in the centre of each vertebra, i.e. vertebrally, while in the Urodela they only occur intervertebrally. The vertebrae in Anura are, as a rule, procoelous. The eighth vertebra is however generally amphicoelous, while the ninth commonly has one convexity in front, and two behind. In some forms such as _Bombinator_, _Pipa_, _Discoglossus_ and _Alytes_ they are opisthocoelous; in others like _Pelobates_ they are variable. THE SKULL[62]. CRANIUM AND MANDIBLE. In the Amphibian skull there are as a rule far fewer bones than in the skull of bony fish. The primordial cartilaginous cranium often persists to a great extent. Only quite a few ossifications take place in it; namely in the occipital region--the exoccipitals, further forwards--the pro-otics, and at the boundary of the orbital and ethmoidal regions--the sphenethmoid. The basi-occipital and basisphenoid are never ossified. As in Mammalia there are two occipital condyles formed by the exoccipitals. Large vacuities commonly occur in the cartilage of both floor and roof of the primordial cranium. These are roofed over to a greater or less extent by the development of membrane bone. Thus on the roof of the cranium there are paired parietals, frontals, and nasals, and on its floor are paired vomers, and a median unpaired parasphenoid. In all living forms the parietals meet and there is no interparietal foramen, though this exists in Labyrinthodonts.