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		Chorioallantoic membrane grafting with chick embryo limb buds Ann Marie Lam and Andy Nichol Swarthmore College and Franklin & Marshall College Objective This experiment explores the ability of the chick chorioallantoic membrane (CAM) to support an excised limb bud from a donor embryo. The chick system will allow observation of general cartilage formation in limb grafts on the chorioallantoic membrane and to study the role of the CAM in calcium transport in ovo.   Introduction Extraembryonic membranes regulate crucial functions in the chick egg, including water retention and gas and ion exchange. Membranes such as the chorioallontoic membrane (CAM) provide a vascular system of blood vessels that facilitate oxygen, calcium, and nutrient transport to the embryo (Tuan, 1987). The chorioallantoic membrane results from the fusing of the mesodermal layer of the allantoic membrane with the mesodermal layer of the chorion which completely surrounds the embryo after 10 days of incubation (Gilbert, 2003). The CAM is attached to the internal surface of the shell membrane and provides a barrier between the watery environment of the embryo and the air space. The structure allows the embryo to harvest the calcium from the shell for bone development. The importance of the shell for supplying calcium is shown in shell-less cultures of chick embryos where the embryos exhibit retarded growth and calcium deficiency (Dunn, 1987). It is estimated that 80% of the 140 mg of calcium found in a hatched chick is derived from the shell (Dunn, 1987). Since the CAM is the primary means of calcium transport between the shell and the developing embryo, it is thus critical for bone formation in normal chick development. Previous experiments have also shown that the CAM can support the development of limb grafts from donor embryos. The vascular CAM transports essential nutrients and gases to the graft, thereby facilitating differentiation and cartilage formation in the limb. This experiment will allow us to study the ability of the chorioallantoic membrane to support development and cartilage formation in limb grafts.