1. Deficiency And Excess Of Development

There are various ways in which arrest of development is manifested in the pelvis. Sometimes the sacrum and coccyx are defective, or altogether absent, or they are stunted in their growth. At other times, one or both of the innominata, or a part of one of them, is wanting, there being at the same time no lower extremities; or a fissure existing in the abdomen may be continued down to the pelvis, and lay open the symphysis. In the siren-monster the lateral parts of the pelvis are fused together.

Allied to this is a pelvis which is of diminutive size, either from its own original conformation, or in consequence of defective growth of the sexual organs or rectum.

Excess of development is exemplified in double monsters, in whom it reaches various degrees.