Secondly, it is a layer of smooth muscle with bundles of circular fibers internal to longitudinal fibers, and thirdly it is an outer layer of connective tissue called the adventitia.
It is a layer of smooth muscle with bundles of circular fibers internal to longitudinal fibers. This is secondly. Secondly it is an outer layer of connective tissue. This is thirdly. This connective tissue is called the adventitia.