A microscopic study of the external carotid artery transitional zone of the adult male dog

Abstract

Structure and length of transitional zone in the dog's external carotid artery was documented. Six normal adult male dogs were studied. The specimens were processed in the routine way by light and electron microscopy. It was established that the transitional zone with 17-mm length contains parallel and fenestrated elastic fibres. In the transitional zone, the elastic fibres in the extracellular space were greater in number than collagen fibres. However, in the non-transitional zone, the rows of smooth muscle cells were greater in number. There were more collagen fibres than elastic fibres in the extracellular space and the elastic fibres appeared to be fragmented. Therefore, the transitional zone showed a structure intermediate between those of elastic and muscular arteries. The involvement of a special structure of transitional zone in vascular disease such as atherosclerosis is suggested.