On Dark Carnival's Stadium Entrance, you can also have another way to summon the Horde. Also in Left 4 Dead 2, there is a new mutation mode called Versus Survival which is a mix of both Survival, and Versus mode.
A serous membrane is a thin membrane that helps body parts move more easily and reduces friction between them. Also known as serosa, these membranes are found throughout the body, usually surrounding organs. There are several medical conditions associated with the serous membane, some of which can be life threatening.
The outer layer of a serous membrane is called the parietal layer and is always attached to the surrounding tissues. The inner layer is called the visceral layer and is firmly attached to the organ it covers. Among the most notable examples of serous membranes are the peritoneum (surrounding the intestines), the pleura (surrounding the lungs), and the pericardium (surrounding the heart).