86 OF THE PELVIS. 



labor be terminated spontaneously, whether the child must be turned, 

 sought for by the hand, or delivered with instruments. 



47. Its principal diameters are four in number: the sacro-pubal, 

 or antero-posterior, which extends from the most salient point of the 

 sacro-vertebral angle to the posterior surface of the symphysis pubis; 

 the transverse or bis-iliac, which passes from the lower edge of one 

 iliac fossa to a point diametrically opposite; the two oblique or mean 

 diameters, which proceed from the sacro-iliac symphysis, and termi- 

 nate behind the ileo-pectineal eminence of the opposite side. 



48. The length of the first or small diameter is, according to 

 Madame Boivin, and most of the French authors, four inches; and 

 four inches and four lines according to Meckel; that of the second 

 is five inches; that of the third from four inches and four lines to 

 four inches and a half: so that their union gives a circumference of 

 about thirteen inches and a half. But these dimensions are subject 

 to great variety, and ought not to be understood here except in a 

 very general manner. 



49. B. Inferior strait. The inferior strait, lesser strait, perineal 

 strait, or apex of the pelvis, is formed by the point and edges of the 

 coccyx, the edges of the sacro-sciatic ligaments, of the tuberosities 

 of the ischium, and the ischio-pubal rami; it accordingly presents 

 three triangular projections, the coccyx behind, and the two ischia 

 on the sides; as well as three indentations, one anterior, very deep, 

 known as the arch of the pubis, and two others, posterior, still deeper 

 and very irregular when the sciatic ligaments are removed, but, on 

 the contrary, quite superficial when these fibrous bands are in their 

 natural situation. Its form is precisely like that of the heart on a 

 playing-card; only it may become oval by the retreat backwards or 

 the removal of the coccygeal triangle; it being in the mean while 

 understood that the widest, most open part of these figures is always 

 turned backwards. 



50. Like the abdominal strait, the inferior strait has four diame- 

 ters: one, the coccy-pubal, or antero-posterior, is measured from the 

 point of the coccyx to the top of the arch of the pubis; another, the 

 transverse, or 6is-ischiatic, from the posterior and interior part of 

 one tuberosity of the ischium to that of the opposite side; the two 

 last, or the oblique diameters, reach from the point where the rami 

 of the pubes and the ischia meet, to the middle of the edge of the 

 sacro-sciatic ligaments. 



51. These diameters are generally found to be four inches each; 

 however, M. Meckel gives to the first four inches and four lines, 

 and four inches six lines to the second. M. Delpech is surely incor- 

 rect in giving as the mean term four inches and a half to one, and 



