Pelvis

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The pelvic girdle of the dinosaur Falcarius utahensis
Human pelvis front image by x-ray (top), magnetic resonance imaging (middle), and 3-dimensional computed tomography (bottom).
Illustration of the Pelvis (Anterior and Posterior view)

The pelvis, derived from the Latin word for "basin", is an anatomical structure found in most vertebrates. This name is given to both:

  • the bony structure that connects the base of the spine to the upper end of the rear legs (in humans, the upper end of the legs), also called the bony pelvis, including the left and right coxal bones, sacrum and coccyx.
  • the region of the body defined by that structure.

The muscles and tissue beneath the bony pelvis are known as the pelvic floor. The rounded epiphysis of the femur, called the Head, articulates with the pelvic bone at a curved cavity in it, called the acetabulum.1 This articulation is called 'the Hip Joint'.

Pelvis skeleton

The skeleton of the pelvis is also known as the bony pelvis, or simply the pelvis. It is a large, bilaterally symmetric, compound bone structure, consisting of:

The top or forward part of the bony pelvis is called the pelvic inlet, and its edge the pelvic brim. A related skeletal structure, found mainly in birds and dinosaurs, is the synsacrum.

In mammals, the bony pelvis has a gap in the middle, significantly larger in females than in males. Babies pass through this gap when they are born.

Pelvic cavity and lesser pelvis

The cavity defined by the bony pelvis up to the pelvic brim, bounded by the pelvic walls is also known as the pelvic cavity. The region of the body defined by the bony pelvis and the pelvic cavity is called the lesser pelvis (or true pelvis).

As the pelvis is concave, another cavity is defined by the pelvis above and in front of the pelvic brim. This is referred to this as the greater pelvis (or false pelvis). Some authors consider it part of the pelvic cavity, others consider it part of the abdominal cavity, others call both the abdominopelvic cavity.

The pelvis has 5 walls :

  • an anteroinferior,
  • a posterior
  • two lateral pelvic walls; and
  • an inferior pelvic wall, also called the pelvic floor.23

Evolutionary history

The pelvis girdle was present in early vertebrates, and can be tracked back to the paired fins of fish that were some of the earliest chordates.4

Evolution in primates

In primates, the pelvis consists of four parts - the left and the right hip bones which meet in the mid-line ventrally and are fixed to the sacrum dorsally and the coccyx. Each hip bone consists of three components, the ilium, the ischium, and the pubis, and at the time of sexual maturity these bones become fused together, though there is never any movement between them. In humans, the ventral joint of the pubic bones is closed.

The most striking feature of evolution of the pelvis in primates is the widening and the shortening of the blade called the ilium. Because of the stresses involved in bipedal locomotion, the muscles of the thigh move the thigh forward and backward, providing the power for bi-pedal and quadrupedal locomotion.5

References

  1. ^ Princeton Review (29 July 2003). Anatomy Coloring Workbook, Second Edition. The Princeton Review. p. 49. ISBN 978-0-375-76342-7. Retrieved 30 July 2012. 
  2. ^ Moore, Keith L. et al. (2010) Clinically Oriented Anatomy 6th Ed., ch. 3 Pelvis and perineum, p.339
  3. ^ Richard S. Snell Clinical Anatomy By Regions, Pevic cavity p.242
  4. ^ William K. Gregory, The American Naturalist, Vol. 69, No. 722 (1935), pp. 193-210, University of Chicago Press. [1]
  5. ^ Bernard Grant Campbell (1998). Human Evolution: An Introduction to Mans Adaptations. Transaction Publishers. p. 170. ISBN 978-0-202-02042-6. Retrieved 30 July 2012. 

External links

  • The dictionary definition of pelvis at Wiktionary
  • Media related to Pelvis at Wikimedia Commons







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