In the sinicipital presentation the large fontanelle is the presenting part; with further labor the head will either flex or extend more so that in the end this presentation leads to a vertex or face presentation. In the brow presentation the head is slightly extended, but less than in the face presentation. The chin presentation is a variant of the face presentation with maximum extension of the head. Non-cephalic presentations are the breech presentation (3.5%) and the shoulder presentation (0.5%). Vertex presentation
The vertex is the area of the vault bounded anteriorly by the anterior fontanelle and the coronal suture, posteriorly by the posterior fontanelle and the lambdoid suture and laterally by 2 lines passing through the parietal eminences. In the vertex presentation the occiput typically is anterior and thus in an optimal position to negotiate the pelvic curve by extending the head. In an occiput posterior position, labor becomes prolonged, and more operative interventions are deemed necessary. The prevalence of the persistent occiput posterior is given as 4.7%.The vertex presentations are further classified according to the position of the occiput, both right, left, or transverse and anterior or posterior:

Left Occipito-Anterior (LOA), Left Occipito-Posterior (LOP), Left Occipito-Transverse (LOT)
Right Occipito-Anterior (ROA), Right Occipito-Posterior (ROP), Right Occipito-Transverse (ROT)The Occipito-Anterior position is ideal for birth; it means that the baby is lined up so as to fit through the pelvis as easily as possible. The baby is head down, facing the spine, with its back anterior.
Medical aspects
Physiological responses
Masters and Johnson were some of the first researchers to study the sexual response cycle in the early 1960s, based on the observation of 382 women and 312 men. They described a cycle that begins with excitement as blood rushes into the genitals, then reaches a plateau during which they are fully aroused, which leads to orgasm, and finally resolution, in which the blood leaves the genitals.In the 1970s, Helen Singer Kaplan added the category of desire to the cycle, which she argued precedes sexual excitation. She stated that emotions of anxiety, defensiveness and the failure of communication can interfere with desire and orgasm. In the late 1980s and after, Rosemary Basson proposed a more cyclical alternative to what had largely been viewed as linear progression. In her model, desire feeds arousal and orgasm, and is in turn fueled by the rest of the orgasmic cycle. Rather than orgasm being the peak of the sexual experience, she suggested that it is just one point in the circle and that people could feel sexually satisfied at any stage, reducing the focus on climax as an end-goal of all sexual activity. Males
As a man nears orgasm during stimulation of the penis, he feels an intense and highly pleasurable pulsating sensation of neuromuscular euphoria. These pulsating sensations originates from the contractions of pelvic floor muscles that begin in the anal sphincter and travels to the tip of the penis, commonly described as a "throbbing" or "tingling" sensation.