18 OBSTETRICS. 



would, in falling downwards, strike on the centre of the symphysis 



pubis. . 



The inclined planes of the pelvis.— These are four m number, an 

 miterior and a posterior on the right side, and an anterior and postenar 

 on the left side. To demonstrate them, let two vertical cuts^be made 

 through the lesser pelvis and at right angles to each other. The first 

 should be made through the symphysis pubis, and the median line 

 of the sacrum and coccyx, and the second, or transverse, should 

 commence behind the tuberosity of the ischium on either side and 

 run upwards perpendicularly through the apex of the spme of the 

 ischium, up to the linea ilio-pectinea. By these two vertical cuts 

 there will be an anterior and posterior inclined plane demonstrated 

 on each side of the pelvis, of which the anterior will be the longer. 



Axes of the pelvis,— There are two axes of the pelvis, one of the 

 brim or superior strait, which is a line drawn perpendicular to the 

 plane of that strait, and, if produced, would extend from the coccyx 

 to a little above the umbilicus ; the other, of the outlet or inferior 

 strait, which is a line drawn perpendicular to the plane of that strait, 

 and if produced, would extend from the promontory of the sacrum 

 to the central space between the tubera ischii. The axes of the upper 

 and lower straits of the pelvis form an obtuse angle with each other. 

 Bv combining these axes with the inclination of the pelvis we can 

 obtain a correct notion of the direction of the canal of the pelvis, 

 which, it will be readily seen, is curved. By havmg a correct know- 

 ledge of the axes of the trunk and pelvic entrance, the obstetrician is 

 enabled to place his patient in the position most favourable to the 

 ready descent of the child's head through the brim into the exca- 

 vation. 



OF THE F(ETAL HEAD. 



The head is of an oval shape, and largest at its occipital ex- 

 tremity ; so that in vertex presentations the largest end necessarily 

 descends first, and its smallest circumference, which is about ten and 

 a half inches, will be nearly parallel to the successive planes of the 

 canal. It is the largest part of the child, and its lateral and superior 

 parietes are most compressible. The bones of the head which re- 

 quire our study are the two parietal, the fro7ital, which is divided 

 into two, the occipital, and the two temporal, for a minute descnption 

 of which, see the division on Anatomy, The bones of the child s head 

 are not dove-tailed into each other as we find them in the adult, but 

 are separated to some extent by intervening lines and spaces ot 

 membiLous formation ; the lines are called .^.^z^r^., the spaces>^. 

 tanelles ; from their having been supposed to distd a "^^isture, they 

 are also called bregmata, from /3ps>, to moisten The sutures are the 

 coronal, sagittaljambdoidal, and squamous. At the two extremities 

 of the sagiSal suture are the two fontanelles, the an^^erior and pos^ 

 terior, named from their position. The anterior is the larger, and is 



