[Anatomical and histological study of the internal carotid artery of sheep]

Studied was the structure of the internal carotid artery of a total of forty newborn and growing lambs, ewes, and rams at the age of up to 8 years, both male and female through preparation, corosion, and histologic methods. Depending on the topography of the artery it could be divided into 3 portions: external, medial, and internal. The medial portion was found to form three S-shaped curves in the tympanic cavity and over the auditory tube. Obliteration was shown to start from the middle portion prior to birth, and it proceeded caudoventrally toward the onset of the artery. During obliteration there were no hyperplastic changes in the three layers of the vessel wall. However, the endothelium underwent certain alteration in that it became similar to the cells of the connective tissue. The internal elastic membrane was disrupted and it gradually disappeared, and the smooth muscle cells of the media resembled the epitheloid and the connective tissue cells. The elastic fibres of the adventitia visibly grew in number. The intracranial portion was found to be of muscle type, having a well developed internal elastic membrane. It retained its connection with the middle portion of the artery during lifetime through a thin branch. It is believed that the obliteration of the artery was the result of disturbed trophism of the arterial wall due to a permanent and continuous pressure of the bones and surrounding tissues in the course of the growth and the particular topography of the artery.