In silat, the surface of the human body is divided into two parts: Jantan and Betina.
Anatomically, jantan is the dorsal area of the body. It is where bone is closest to the surface and normally has more body hair like the tops of your forearms, the elbows, the shoulders, the back, the spine, the tops of the thighs, the knees, the shins and the tops of the feet, the cheeckbones, the forehead and the back of the head.
Betina is known as the ventral area where the nerves and arteries are closer to the surface like the palms, the wrists, the underside of the arm, the armpit, the chest and abdominal area, the genitals, inside of the thighs, the calves, the eyes and the face.
Most silat styles teach you to attack the ventral areas as they tend to incur the highest damage, while the dorsal areas are to be avoided as they normally contain hard weapons like the fist, elbow and knee.
Relevance to body language exists in the belief that the more we trust someone, the more we allow them into our ventral area (opening up). The more we distrust someone, the more we close up with our ventral areas. This comes from growing up and learning physical rewards and damage from childplay.
As a child, you realise that impact to your ventral areas (falling face down, getting kicked in the genitals, bumping your inner thigh on a table corner) hurts more than impact to dorsal areas. Thus, when you protect yourself, the instinct is to cover up as much of the ventral as possible.
Even without learning martial arts, a person being beaten will curl up into a ball to expose as much dorsal and protect as much ventral.