502 
DEPARTMENT OF SURGERY. 
Diagrammatic sagittal section through dilated vagina of mare. A, Aorta ; R, rectum; U, 
uterus ; V, vagina ; /, vaginal incision. 
the median line, the blade being held vertical, that is, the cut¬ 
ting surface parallel to the longitudinal muscular fibres of the 
vagina, and guarding the possible extent of its introduction 
with the thumb and fingers, push it directly forward in a 
straight line with a quick thrust through vaginal mucosa, the 
muscular walls and the peritoneum until the disappearance of 
resistance indicates that the peritoneum has been penetrated. 
This is the most critical step in the operation. The vagina of the 
mare possesses the property of dilating in a remarkable manner 
like a balloon filled with air, occupying at such times practi¬ 
cally the entire pelvic cavity, the rectum collapsed, and the 
roof of the vagina stretched firmly against the sacrum and in 
