The problem of uterine activity during labor, more particularly as regards the regularity of contraction and relaxation, has from time immemorial attracted the attention of the medical profession. Yet if one reviews what is known or conjectured concerning the nervous and hormonic principles that may govern the underlying biologic processes, one is confronted with such bewildering divergence of opinion that it is difficult to form a conception of the pathways for the conveyance of the nervous impulse to the pregnant organ. Bearing in mind that an appreciation of function presupposes a thorough knowledge of structure, it seemed advisable to approach the object in view by a careful study of the histology of the pregnant uterus, devoting special consideration to its outer layer. It is this stratum which in the past has challenged the attention of several investigators. While there still exists a great deal of controversy concerning the anatomic structure