In the popular mind, mass extinctions are associated with catastrophic events, like giant meteorite impacts and volcanic super-eruptions. But the worldâs first known mass extinction, which took place about 540 million years ago, now appears to have had a more subtle cause: evolution itself. âPeople have been slow to recognize that biological organisms can also drive mass extinction,â said Simon Darroch, assistant professor of earth and environmental sciences at Vanderbilt University.
The pectoralis major (/ËpÉktÉËreÉªlÉ¨s ËmeÉªdÊÉr/) (from Latin: pectus, breast) is a thick, fan-shaped muscle, situated at the chest (anterior) of the human body. It makes up the bulk of the chest muscles in the male and lies under the breast in the female.he pectoralis major (/ËpÉktÉËreÉªlÉ¨s ËmeÉªdÊÉr/) (from Latin: pectus, breast) is a thick, fan-shaped muscle, situated at the chest (anterior) of the human body. It makes up the bulk of the chest muscles in the male and lies under the breast in the female.
The lumbar plexus is what separates the superficial part from the deep part. The psoas major assists with the flexion and external rotation of the hip joint. It is also considered part of the group of muscles that are known as the hip flexors. If this muscle tightens, the action may result in lower back pain.soas major. The psoas major is a lengthy fusiform (or âspindle-shapedâ) muscle that can be found on the side of the lumbar region of the vertebral column. It is also adjacent to the brim of the lesser pelvis area.