182 TOPOGRAPHICAL ANATOMY OF THE 



completely surroundeii by unyielding bone, its measurements are of 

 surpassing importance. The obstetrician recognises four diameters of 

 the inlet — a conjugate, a transverse, and right and left oblique. (1) 

 The conjugate diameter is measured from the middle of the sacral 

 promontory to the cranial end of the symphysis of the hip-bone. (2) 

 The transverse diameter is the greatest width of the inlet, which, in a 

 well-formed pelvis, is immediately dorsal to the psoas tubercles. (3) 

 The oblique diameters (of minor moment) are measured from one 

 sacro-iliac articulation to the ilio-pectineal eminence of the opposite 

 side. The caudal aperture (outlet) of the pelvis n)ay be measured in a 

 similar luiuiner. 



The axis pelvis is a line that passes through the centre of the 

 plane of the cranial and caudal apertures, and through the centre of a 

 series of transverse planes between these. The term inclination of the 

 pelvis (inclinatio pelvis) indicates the obliquity at which the plane of 

 the inlet is set to the long axis of the body. 



There are certain ditfereuces between the male and female pelvis, 

 to the most important of which reference must be made. The whole 

 pelvic cavity is more spacious in the mare than in the stallion, and the 

 diameters of the inlet are appreciably greater. The inclination of the 

 pelvis is more marked in the female than in the male, as can be best 

 indicated by saying that a perpendicular erected from the cranial border 

 of the pubis would strike the fourth sacral vertebra in the female and 

 the second in the male. The outlet is larger in the female, mainly 

 because of the greater width of the sciatic arch. 



Dissection. — Proceed as in the dissection of the male pelvis. 

 Constant reference must be made to page 156 et seq., for it must be 

 understood that the following paragraphs deal with the points only in 

 which the female structures differ from those of the male. Where no 

 difference is stated, the descriptions as given for the male are applic- 

 able to the female. 



Female genital organs. — The reproductive organs of the female 

 consist of two ovaries with their associated uterine tubes, the uterus, 

 the vagina, the vestibule of the vagina,^ and the external genital parts 

 or vulva. Of these the ovaries, uterine tubes, and the greater part of 

 the uterus are abdominal in position, and have been examined at an 

 earlier stage in the dissection. 



The vagina^ is a very dilatable tubular organ, about 20 cm. in 

 length, connecting the uterus and the vestibule.^ Except for a short 



' Some writers include the vestibule witli the vulva. 



- Vagina [L.], a sheath. 



^ Externally there is no line of demarcation between the uterus and vagina or 

 between the vagina and the vestibule. By palpation, however, it is easy to determine 

 the position and limits of the neck of the uterus by its firm resistance. 



