86 



OBSTETRICS. 



turned upwards into the costa of the ilium, while the shoulder de- 

 scends or engages in the superior strait. 



Diagnosis. — It is only when the labour has commenced, and 

 indeed made some progress, that a shoulder presentation can be 

 positively detected. It may be suspected, if we are unable to reach 

 the presenting part, if the os uteri, though flaccid, opens slowly, if 

 the bag of waters is cylindrical, or like the finger of a glove, and if 

 the uterus ceases to act after the membranes have been ruptured for 

 some time. We can only positively detect the presentation by dis- 

 tinguishing the different parts of the child, as, for instance, the 

 spinous process of the scapula, the clavicle, the round-shaped 

 shoulder, the axilla, the ribs, the arm, and in some eases the hand 

 when prolapsed, distinguished from the foot by the means already 

 pointed out. The aspect of the palm of the hand will mark whether 

 it be the right or left. The diagnosis between the breech and the 

 shoulder' will be easy, if the distinguishing marks of the former are 

 remembered. 



Positions. — There are two positions for the presentation o? each 

 shoulder, viz., Ql first and second for the right shoulder ; and a first 

 and second for the left. In both the first positions the head is on the 

 left of the mother, and in both the second, on the right. As shoulder 

 presentations are deviations from vertex presentations, the fi^rst posi- 

 tions are the most common. These positions are called the dorso- 

 pubic and dorso-sacral of the right, and dorso-sacral and dorso-pubic 

 of the left shoulder. 



Fig. 27. 



