774 Veterinary Obstetrics 



parently normal position, until the anterior portions have passed 

 beyond the vulva and the hips of the fetus have reached the 

 pelvic inlet, when the progress is interrupted and the fetus re- 

 fuses to move, even under vigorous traction. The interpretation 

 of this condition varies with different obstetrists. 



Some hold that the dystokia occurs because the two stifles are 

 in a state of abduction and thus, standing apart, catch upon the 

 pelvic margin and stop the progress of the fetus. It is difficult 

 to conceive of the possibility of such a condition, because there 

 is nothing to maintain such abduction, but all the expulsive 

 forces tend to promptly and effectively overcome it. 



According to our interpetation of this difficulty, the conditions 

 are as we have depicted in Fig. 109, page 650, and consist es- 

 sentially of the interlocking of the pelves of the fetus and mother 

 in such a way that, if the traction is applied in a somewhat unfa- 

 vorable upward direction, the incarceration is emphasized instead 

 of being overcome. 



During its development the embryo lies in the form of the seg- 

 ment of a circle, and the ventral surface of the body is main- 

 tained in a somewhat concave form. When the fetus begins its 

 passage through the birth canal, it maintains this curved form 

 until it has been completely expelled from the vulva. If this 

 direction becomes interrupted, according to our observation, the 

 pelvis of the fetus may become interlocked with that of the 

 mother. 



If, when the chest of the fetus is passing through, or has 

 passed beyond the vulva, traction is directed upward instead of 

 downward, the external tuberosities of the fetal ilia are thrown 

 upward, and the prepubian tendon of the fetus, being rendered 

 tense, draws the fetal pubis forward, flexes the fetal pubis upon 

 the sacrum and increases the transverse diameter between the 

 supero-external tuberosities of the fetal ilia. 



The tension upon the prepubic tendon, by advancing the fetal 

 pubis, increases greatly and dangerously the perpendicular 

 diameter of the fetal pelvis. Normally the fetal pelvis leaves the 

 spinal column at an acute angle, and, if traction is exerted on 

 the spine, this angle is increased, the ilial tuberosities are low- 

 ered, and the ischia and pubis pass backwards and upwards. If 

 the traction is instead applied to the pubis through the prepu- 

 bian tendon, the angle is reduced and the ilial shafts approach 



