This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal Skull and Maternal Pelvis, Subject name: Gynaecology & Obstetrics
If both the ala of the sacral bone are absent, pelvis is called as: 
Select and explain. 
A. Naegele pelvis, B. Robert pelvis, C. Triradiate pelvis, D. Rachitic pelvis
B: Robert pelvis
Answer: B: Robert pelvis 
Explanation: Ans. is b, i.e. Robert pelvisRef. Dutta Obs. 9/e, p 326If one ala is absent-pelvis is called Naegle's pelvis.If both ala of succumb are absent-pelvis is called as Robert's pelvis.Both are varieties of contracted pelvis and in both cesarean section is done.