Moroccan riad been bought by foreigners. This foreign interest has brought new challenges but the investment has helped with the restoration of the UNESCO site and has helped revive many of the handcrafts and artisan trades that were gradually being lost before this trend. Many of the restored riads in the districts of Mouassine and Lakssour offer the finest examples of restoration as historically these areas contained many of the grand palaces from Marrakech's Saadian period. Moroccan riad A riad () is a type of traditional Moroccan house or palace with an interior garden or courtyard. The word riad originates from the
Atrium (heart) similar function. Some animals (amphibians and reptiles) have a three-chambered heart, in which the blood from each atrium is mixed in the single ventricle before being pumped to the aorta. In these animals, the left atrium still serves the purpose of collecting blood from the pulmonary veins. In some fish, the circulatory system is very simple: a two-chambered heart including one atrium and one ventricle. Among sharks, the heart consists of four chambers arranged serially (and therefore called a serial heart): blood flows into the most posterior chamber, the sinus venosus, and then to the atrium which moves it to