has part has part has_part anterior to posterior to mesocoxal muscle neck membrane insect thorax The hind leg muscles sometimes attach to the second abdominal sternite. The abdominal sopiracles are different in their structure from tghe thoracic spiracles as they are opened and closed by two articulating sclerites that are moved by two sets of muscles whereas the thoracic spiracles are closed by only one occlusor muscle and opened by the flexibility of the distal tracheal region. The border between the thorax and the abdomen is sometimes marked by the anterior first abdmonial tergal conjunctiva. In Hymenoptera, the border between the abdomen and the thorax cannot be defined as the anterior first abdmonial tergal conjunctiva is absent, the sclerite that receives muscles from the metacoxa also contains the first abdominal spiracle. The region of cuticle that is connected to some muscles of the fore and hind legs and is posterior to the neck membrane and aterior to the first abdominal spiracle. insect abdomen procoxal muscle region of cuticle prothorax mesothorax metathorax insect tagmatic subdivision of integument