The diapophyses of the sacral vertebra carry no ribs, the ilia being attached to them directly. They are either cylindrical {22}as in the Ranidae and Cystignathidae, or they are more or less dilated as in all the other families, most strongly in the Pelobatidae and the Aglossa. In some members of the large sub-family of the Cystignathidae the otherwise cylindrical diapophyses are slightly dilated. [Illustration: FIG. 4.–Dorsal view of the sacral or ninth vertebra (9), with the attachment of the ilium, of (1) _Rana temporaria_, (2) _Bufo vulgaris_, showing the whole coccyx and pelvis, (3) _Pelobates fuscus_, as examples of cylindrical and of dilated sacral diapophyses. (About nat. size.) _a_, Acetabulum; _c_, coccyx; _i_, ilium; _z_, anterior zygapophyses.] The sacrum is formed by the ninth vertebra, but there are a few interesting exceptions. _Pelobates_, _Pipa_, and _Hymenochirus_ possess two sacral vertebrae; and, neglecting individual abnormalities, these three genera form the only exception amongst recent Amphibia. In the three genera the coccyx is fused with the second sacral vertebra, and such a fusion occurs elsewhere normally only in _Bombinator_ with its single sacral vertebra. The morphologically oldest condition is normally represented by _Pelobates_, the sacral vertebrae being the tenth and ninth. One case has been recorded by Boulenger of _Bombinator pachypus_ "with eleven segments," the last carrying the ilium. Individual lop-sided abnormalities have been described in _Bombinator_ and _Alytes_, where the right ilium articulated with the tenth, the left ilium with the ninth vertebra. This shifting forwards of the ilium to the extent of one metamere has been continued further in _Pipa_, in which the sacrum is formed by the ninth and eighth vertebrae, their diapophyses fusing on either side into extra broad wing-like expansions. In old specimens of _Palaeobatrachus fritschi_ the seventh vertebra is in a transitional condition, the ilium being carried by the ninth and eighth, and slightly also by the diapophyses of the seventh vertebra; and in _P. diluvianus_ the {23}diapophyses of all these vertebrae are united into one broad plate to which the ilia are attached. Lastly, in _Hymenochirus_ the first sacral is the sixth vertebra, and this creature has thereby reduced the pre-sacral vertebrae to the smallest number known.