In uniparous animals rotation is in the nature of an accommodation of the greatest diameter of the fetal body in cross section to greater axis of the mother—the dorsoventral. Uterine contractions cause the fetus to unfold from its elliptical form and to assume an extended position, permitting head or breech to enter the lower pelvis. The pubic angle having been passed and the extension of the presenting part being successfully accomplished, there is no striking difference in the manner of external expulsion of the fetus. DYSTOCIA. Dystocia in domesticated animals is a well studied subject, and its general clinical phases are fairly well known. Several cases have been observed, details of which are worthy of note since some of them are entirely complete. Inertia uteri as a single non-obstructive condition seems not to have been observed here, although well enough known to veterinarians. Nor has a case of dystocia been seen as the result of excessive expulsive force. Obstruction to natural passage by bony deformities or malformations is a common occurrence in man but not so in lower animals. There may also be dystocia by reason of a normally formed but too small pelvis when the female has been impregnated by a much larger male, or if the female conceived before the pelvis has achieved its full growth. Deformities may be due to irregularities of bony development, exostoses, fracture or diseases of the osseous system. A most interesting case of this type occurred in a Barbary ape (_Macacus innuus_) which had been in the collection for two years and was apparently in good health when discovered in labor. No progress being made and the animal becoming shocked, an ineffectual attempt was made to deliver by version, the monkey dying during the operation. Upon autopsy the uterus contained a fetus apparently at term. The head was extended so that the face presented, but the head was not engaged. The cervix was fully dilated but the uterine muscle was relaxed and flaccid. The fetus was dead when the animal was first examined. The uterus contained two placentæ as is normal for these apes, the left placenta being the place of attachment of the fetus while the right one was somewhat smaller and presented no umbilical cord. The fetus was normal in size and form, the face was extended and its lower portion far advanced in a caput succedaneum. The measurements of the fetal were as follows: bitemporal 5.5 cm., biparietal 6 cm., occipitomental 8.5 cm., occipitofrontal 7.5 cm. The pelvis (dried specimen) presents a most interesting condition. The sacrum is bent sharply forward, carrying with it the border of the ilia, which are bent upon themselves forward and downward. The lateral walls of the pelvis are greatly narrowed, the ischia drawn inward. The pubes and the symphysis are fairly normal. The pelvic measurements are: diagonal conjugate 6 cm., true conjugate 4 cm., greatest transverse 4 cm.