"If, upon such an examination, it should be ascertained that the os uteri is considerably dilated, and the child cannot be felt, this affords reason to suspect that the presentation is preternatural. Should the liquor amnii be discharged and the child be out of reach of the finger, the probability of a preternatural position is greater. Should the membranes be found hanging down in the vagina not of the usual globular form, but rather conical and small in diameter, this likewise is a presumptive proof of a cross-birth; especially if there be any part presenting through the membranes which is smaller, feels lighter, or gives less resistance when touched than the bulky heavy head."[109] The diagnosis of the shoulder is by no means easy: it offers no distinctive marks, and may readily be mistaken for the nates, or even for the head. It feels round, but is smaller and softer than the head. The scapula and clavicle, the neck, the armpit, the arm itself, and the ribs, assist us in our diagnosis. From the direction of these parts, we shall be able to ascertain the position of the rest of the body, and which shoulder presents. If the hand has prolapsed, the direction of the palm and of the thumb will soon show the position of the child. Labours with malposition are always dangerous; when left without assistance, they are almost always fatal to the child, and generally so to the mother. When a full-grown child has presented with the arm or shoulder, and nothing has been done to assist the delivery of it, the results are usually as follow:--After the membranes have burst, and discharged more liquor amnii than in general where the head or nates presents, the uterus contracts tighter around the child, and the shoulder is gradually pressed deeper into the pelvis, while the pains increased considerably in violence, from the child being unable, from its faulty position, to yield to the expulsive efforts of nature. Drained of its liquor amnii, the uterus remains in a state of contraction even during the intervals of the pains; the consequence of this general and continued pressure is, that the child is destroyed from the circulation in the placenta being interrupted, the mother becomes exhausted, and inflammation or rupture of the uterus or vagina are almost the unavoidable results.