diameter /di·am·e·ter/ (di-am´ĕ-ter) the length of a straight line passing through the center of a circle and connecting opposite points on its circumference. Symbol d.
anteroposterior diameter the distance between two points located on the anterior and posterior aspects, respectively, of the structure being measured, such as the true conjugate diameter of the pelvis or occipitofrontal diameter of the skull.
Baudelocque's diameter external conjugate d.; see pelvic d.
conjugate diameter see pelvic d.
cranial diameters distances measured between certain landmarks of the skull, such as biparietal, that between the two parietal eminences; bitemporal, that between the two extremities of the coronal suture; cervicobregmatic, that between the center of the anterior fontanel and the junction of the neck with the floor of the mouth; frontomental, that between the forehead and chin; occipitofrontal, that between the external occipital protuberance and most prominent midpoint of the frontal bone; occipitomental, that between the external occipital protuberance and the most prominent midpoint of the chin; suboccipitobregmatic, that between the lowest posterior point of the occiput and the center of the anterior fontanel.
pelvic diameter any diameter of the pelvis, such as diagonal conjugate, joining the posterior surface of the pubis to the tip of the sacral promontory; external conjugate, joining the depression under the last lumbar spine to the upper margin of the pubis; true (internal) conjugate, the anteroposterior diameter of the pelvic inlet, measured from the upper margin of the pubic symphysis to the sacrovertebral angle; oblique, joining one sacroiliac articulation to the iliopubic eminence of the other side; transverse (of inlet), joining the two most widely separated points of the pelvic inlet; transverse (of outlet), joining the medial surfaces of the ischial tuberosities. 
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Diameters of pelvic inlet (see also pelvic planes ).
| anteroposterior diameter n. See conjugate. |
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