Engaging diameter if the vertex is markedly deflexed is -

Ans. is 'a' i.e., OccipitofrontalDiametersMeasurement in cm (inches)Attitude of the headPresentation1. Suboccipito-bregmatic-extends from the nape of the neck to the center of the bregma9[?]5 cm (3 3/4 ")Complete flexionVertex2. Suboccipito-frontal- extends from the nape of the neck to the anterior end of the anterior fontanelle or centre of the sinciput10 cm (4")Incomplete flexionVertex3. Occipito-frontal - extends from the occipital eminence to the root of the nose (Glabella).11[?]5 cm (4 1/2 ")Marked deflexionVertex4. Mento-vertical - extends from the mid point of the chin to the highest point on the sagittal suture14 cm (5 1/2 ")Partial extensionBrow5. Sybmento-vertical - extends from junction of floor of the mouth and neck to the highest point on the sagittal suture11[?]5 cm (4 1/2 ")Incomplete extensionFace6. Submento-bregmatic - extends from junction of floor of the mouth and neck to the centre of the bregma9-5 cm (3 3/4 ")Complete extensionFace