The adventitia varies much in thickness, being better developed in the medium-sized than in the large arteries.
Up to the third decade there is only a strengthening of the media and adventitia.
Coincidently with this, there is thickening by a connective tissue growth in the adventitia.
There is also, as a rule, rather pronounced hypertrophy of the adventitia.
adventitia ad·ven·ti·tia (ād'věn-tĭsh'ə, -vən-)
The outermost membranous covering of an organ or structure, especially the outer coat of an artery.