On the Female Organs and Placentation of the Racoon. 277 



in thickness involved both the muscular and mucous coats, arid 

 is doubtless to be attributed to mechanical distention of the horn by 

 the contained ovum. The mucous membrane presented no trace of 

 the well-defined transverse rugee met with in the horn of the other 

 side, and was of a softer and more succulent texture. On careful 

 examination, however, this membrane was seen to be thrown into 

 numerous very minute tortuous and anastomosing folds, which closely 

 resembled those described and figured by Professor Turner in the 

 impregnated uterus of Orca gladiator.* These folds were more dis- 

 tinctly marked at the placental site than in other parts of the horn, 

 where the mucous membrane was almost smooth. The more minute 

 description of the microscopic structure of the uterine mucous mem- 

 brane, together with the modifications which it undergoes in the 

 impregnated horn, will be deferred till after the consideration of the 

 ovum and placenta. 



Although the corpus uteri is not distinguishable externally from 

 the vagina, yet upon examining the interior of the cavity the position 

 of the os uteri is seen to be clearly defined by a well-marked valve- 

 like projection of the mucous membrane. This valve consists of two 

 segments, an anterior and a posterior, which, however, are continuous 

 with one another, so that the entire structure presents an annular 

 character. The central portion of each segment of the valve measures 

 half an inch in breadth, whilst laterally, where it becomes continuous 

 with its fellow, each segment diminishes to quarter of an inch in breadth. 

 The two segments together form a circular valve attached to the entire 

 circumference of the uterus, and prolonged superiorly and inferiorly 

 into two points which project backwards into the lumen of the vagina. 

 The mucous membrane of the body of the uterus is thrown into 

 slight longitudinal rugee, which commence opposite the free margin 

 of the septum uteri, and extend along the whole length of the organ. 



The diameter of the vagina, as already mentioned, is the same as 

 that of the corpus uteri ; and although, therefore, there is no distinct 

 line of demarcation between these two portions of the genital appa- 

 ratus visible externally, an examination of the interior of the organ 

 shows that the limits of both are clearly enough defined. In fact, 

 the separation of the corpus uteri from the vagina is indicated by 

 the annular valve above described as corresponding in position to the 

 os uteri ; whilst, posteriorly, the vagina is distinguished from the uro- 

 genital canal by the position of the urethral orifice, as well as by a 

 slight fringe-like fold of mucous membrane, which is attached to the 

 entire circumference of the vaginal canal. The mucous membrane of 

 the latter is thrown into slightly marked longitudinal ruga? which, 

 however, are of larger size than those met with in the body of the 

 uterus. 



* " Lectures on the Comparative Anatomy of the Placenta," p. 45. 



