Question

) The ileac blade provides attachment areas for the Gluteus medius and Gluteus minimus muscles.  They “originate” here; they “insert” into the neck and lateral trochanter of the femur, and when they contract, they pull in more or less a straight line between their origin and their insertion (the origins and insertions are marked on the cast of a full human skeleton; you can also see them on the figures in the study guide).  Look again at the shape and orientation of the ileac blade, and also look at the chimpanzee skeleton and that of a human and compare how the ileum is oriented with respect to the spinal column.  In which is it along/parallel to the spinal column?  What is its relative placement and orientation in the other?  In which direction would these muscles pull a chimpanzee’s leg when they contract?  What motion do you think they cause when they contract in humans?

Answer 1

The human pelvis is one of the important part of skeletal system. It supports and transmits the body weight to lower limbs to maintain balance during walking.
The human pelvis has evolved greatly according to the adaptation of humans.
The pelvis consists of the right and left hip bone and the sacrum joining the 2 bones.
Hip bone consists of ilium, ischiuma and pubis. It provides attachment to various muscles.
- Iliac blade shape and orientation in humans : The iliac blades in humans are shorter compared to chimpanzees. They are oriented in a way to allow lumbar lordosis which helps lower centre of mass. This allows bipedal walking in humans. In humans iliac blades exhibit curve laterally and flare outward. This makes the pelvis bowl shaped. This arranged of iliac crest and the shape of pelvis allows the gluteal medius and minimus to cross laterally over the hip and help them in hip abduction. During the human gait cycle when the body is supported by a single leg, the gluteal muscles cause pelvic drop on the unsupported side and pelvic hike on the supported side to maintain balance.
Shape and orientation in chimpanzees: iliac plate in chimpanzees is more tall and flat and oriented more parallel. The gluteals arise from the external surface of ilias crest and run posteriorly over the hip. They act as hip extensors. This results in side to side flexion of trunk while walking bipedally instead of pelvic shift to maintain balance. This is more energy consuming.