Pectus carinatum is an overgrowth of costal cartilage causing the sternum to protrude forward. The splits in the vertebrae are so small that the spinal cord does not protrude. The stamens protrude 2 to 3 millimeters. A series of push rods protrude from the snout. In some cases, the rectum may protrude. If pedunculated, they can protrude through the cervix into the vagina. Abdominal contents may protrude through the ring in inguinal hernia. The chloroplast membranes sometimes protrude out into the cytoplasm, forming a stromule, or stroma-containing tubule. The lower teeth normally protrude further than their upper, resulting in an under-bite. The lips protrude in a thin pout. These coiled-coils protrude from the hexameric ring. Nests are considered mounds if they protrude from the earth's surface. Oocysts protrude from the surface of stomach, giving it a blistered appearance. The short antennae protrude between the eyes or in front of them. The cystic spaces have epithelium referred to as papillary infoldings that protrude into them.