| Pubis (bone) | |
| Latin: | os pubis |
| Partof: | Pelvis |
In vertebrates, the pubis or pubic bone (Latin: os pubis) forms the lower and anterior part of each side of the hip bone. The pubis is the most forward-facing (ventral and anterior) of the three bones that make up the hip bone. The left and right pubic bones are each made up of three sections; a superior ramus, an inferior ramus, and a body.
The pubic bone is made up of a body, superior ramus, and inferior ramus . The left and right coxal bones join at the pubic symphysis. It is covered by a layer of fat – the mons pubis. The pubis is the lower limit of the suprapubic region. In the female, the pubis is anterior to the urethral sponge.
The body of pubis has:
The body forms the wide, strong, middle and flat part of the pubic bone. The bodies of the left and right pubic bones join at the pubic symphysis.[1] The rough upper edge is the pubic crest, ending laterally in the pubic tubercle. This tubercle, found roughly 3 cm from the pubic symphysis, is a distinctive feature on the lower part of the abdominal wall; important when localizing the superficial inguinal ring and the femoral canal of the inguinal canal.[2] The inner surface of the body forms part of the wall of the lesser pelvis and joints to the origin of a part of the obturator internus muscle.
The superior pubic ramus is the upper of the two rami. It forms the upper edge of the obturator foramen.[3] It extends from the body to the median plane where it joins with the ramus of the opposite side. It consists of an inner flattened part and a narrow outer prismoid portion.
The upper border presents a prominent tubercle, the pubic tubercle (pubic spine), which projects forward; the inferior crus of the subcutaneous inguinal ring (external abdominal ring), and the inguinal ligament (Poupart's ligament) are attached to it.
Passing upward and laterally from the pubic tubercle is a well-defined ridge, forming a part of the pectineal line which marks the brim of the lesser pelvis: to it are attached a portion of the inguinal falx (conjoined tendon of obliquus internus and transversus), the lacunar ligament (Gimbernat's ligament), and the reflected inguinal ligament (triangular fascia).
Medial to the pubic tubercle is the crest, which extends from this process to the medial end of the bone. It affords attachment to the inguinal falx, and to the rectus abdominis and pyramidalis.
The point of junction of the crest with the medial border of the bone is called the angle; to it, as well as to the symphysis, the superior crus of the subcutaneous inguinal ring is attached.
The medial border is articular; it is oval, and is marked by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of a thin layer of cartilage, which intervenes between it and the interpubic fibrocartilaginous lamina.
The lateral border presents a sharp margin, the obturator crest, which forms part of the circumference of the obturator foramen and affords attachment to the obturator membrane.
The inferior pubic ramus is a part of the pelvis and is thin and flat. It passes laterally and downward from the medial end of the superior ramus; it becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen.
Non-placental mammals possess osteological projections of the pubis known as epipubic bones. These evolved first among derived cynodonts, and evolved as a means of support for muscles flexing the thigh, facilitating the development of an erect gait.[4] However, these prevent the expansion of the torso, preventing pregnancy and forcing the animal to give birth to larval young (the modern marsupial "joeys" and monotreme "puggles").[5]
Placentals are unique among all mammals, including other eutherians, in having lost epipubic bones and having been able to develop proper pregnancy. In some groups, remnants of these pre-pubic bones can be found as os penises.[6]
The clade Dinosauria is divided into the Saurischia and Ornithischia based on hip structure, including importantly that of the pubis.[7] An opisthopubic pelvis is a condition where the pubic bone extends back towards the tail of the animal, a trait that is also present in birds.[8] In a propubic pelvis, however, the pubic bone extends forward towards the head of the animal, as can be seen in the typical saurischian pelvic structure pictured below. The acetabulum, which can be thought of as a "hip-socket", is an opening on each side of the pelvic girdle formed where the ischium, ilium, and pubis all meet, and into which the head of the femur inserts. The orientation and position of the acetabulum is one of the main morphological traits that caused dinosaurs to walk in an upright posture with their legs directly underneath their bodies.[9] The prepubic process is a bony extension of the pubis that extends forward from the hip socket and toward the front of the animal. This adaptation is thought to have played a role in supporting the abdominal muscles.