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.
Pectoralis major. A chest muscle that pulls the arm in towards the body. This is one of the internal rotator muscles that attach the humerus and internally rotate the arm. The pectoralis major originates along the clavicle, down the sternum, and across the ribs and inserts into the humerus.s a diagonal muscle that tightens the abdomen. Itâs the largest and the most outermost of the three flat muscles of the outside front of the abdomen. It has limited actions in both flexion and rotation of the vertebral column.