Marwa-Babiker A.M., Ali H. A., Ismail H.I.

The histological structure of the sinoatrial node (SAN) in the dromedary camel foetus was investigated using routine histological techniques and some special stains. Twenty foetuses were used. They were divided into two groups 10 foetuses were in the second trimester (131-260 days); the rest in the third trimester (261-423.5 days of gestation). Samples were collected from the right atrium cranial to the opening of cranial vena cava. The SAN in the camel foetus was found in subepicardial region cranial to the opening of cranial vena cava at the junction between the cranial vena cava and right atrium. Two types of cells were observed; the first type had dark cytoplasm and large spherical lightly stained nucleus. The cells of the second type were small and spindle in shape with dark small nuclei. It is concluded that SAN in camel foetuses in the second and third trimesters had the same location as in the adult and also had two types of cells as in other animal species.