The contractions of the monkey uterus at term

Abstract

1.1. The present study, while far from complete, records for the first time the manner in which the wave of contraction passes over the parturient uterus simplex of the monkey. Presumably a similar action characterizes the very comparable human uterus.2.2. From a constantly quiescent area slightly ventral and cranial to the insertion of the tubes, elliptical, concentric waves of contraction pass medially to meet in the midline and cranial border of the uterus, passing caudally, then involving the lower segment and finally the cervix uteri.3.3. Such contractions, after they reach the midline, follow the conducting bundle postulated by Hofbauer (1930) (not macroscopically demonstrable in the monkey). The contractions pass as we would expect on the basis of the homologies outlined above as well as the embryologic development of the parts of uterus and tubes. The placental site is less involved by contractions than the remainder of the uterus.4.4. The homologies referred to suggest that the lower segment of the primate uterus represents the corpus of bicornuate uteri; the upper segment the fused horns, the contraction ring, the cornual sphincters. This view is supported on both anatomic and physiologic grounds.5.5. The musculature of the cervix is chiefly concentrated into a powerful sphincter at the internal os, which may be felt by the examining finger from the lumen side and may be seen externally (see Figs. 2 and 3). This sphincter is of the greatest obstetric importance, at least in the monkey. Upon delivery the uterus contracts maximally, forming the typical picture seen in Figs. 2 and 3. Contraction is greatest in the region of the placental sites, which further reduces the dangers of hemorrhage.6.6. The pregnant and the parturient uterus are relatively nonirritable to nerve stimulation.7.7. Stimulation of the mammary nipples causes a slight increase in the rate of the contractions.8.8. Pituitrin (pitocin), in the dosage employed, causes spastic contractions over the entire uterus, followed by intermittent contractions without full relaxation. The contraction wave of normal sequence does not occur, hence the contractions after pitocin are little calculated to expel the fetus.9.9. Adrenalin causes a primary contraction followed by temporary quiescence. It also abolishes the contraction due to pituitrin or ergotamine, gotamine, the latter of which had only a mild action in the doses employed.