A. The right Ilium.--B. The Sacrum.--C. The Coccygis.--_b._ The Os Pubis.--_c._ The Os Ischinum.--_g._ The Foramen Magnum.--_o._ shows the manner in which the coccygis is bent back through labor.] These bones are all firmly bound together by a cartilaginous substance, which is placed between where they touch, and is firmly attached to each one. This union is called a _symphysis_. The one at front which joins the pubic bones is called the symphysis pubis; the two which join the Ossa Illii to the Sacrum are called the sacro iliac symphyses; and that which joins the Coccygis to the Sacrum, is called the Sacro coccygeal symphysis. The two pubic bones are separated a little in Plate VIII, simply to show them better. The reader will bear in mind that they are naturally connected by the cartilaginous substance which forms the symphysis. These articulations, or joinings, become much softened during labor, and give way a little, but not to any extent sufficient to assist delivery. It is a mistake to suppose that the bones separate at that time. The only part which gives way is the sacro coccygeal symphysis, which does relax, and allows the Os Coccygis to be pushed back by the child's head a full inch or more, thus enlarging the inferior strait.--(See _c._ and _o._ Plate VIII.) Sometimes this little bone will be even broken off, when there is great disproportion between the head and the strait. I have heard it snap like a stick breaking. There is nothing serious nor alarming in this, however, unless it be _a first delivery late in life_, though it may cause some pain at the time, and a little difficulty in _sitting_ for some time after. In young persons the symphysis is soft, and gives way easily, so that they have little difficulty during delivery from this cause; but if a female marry late in life, after it becomes hardened, she may suffer considerably. In this case the coccygis is usually curved inwards considerably, and being firmly fixed the head cannot push it back, and on that account cannot pass, without great difficulty, and with the risk of rupturing some of the soft parts, or breaking the coccygis completely off. There is in fact great difficulty, and some danger, if the first pregnancy takes place late in life. The Pelvis is usually divided into two parts,--the _great pelvis_, or upper part, enclosed between the wide flanges of the Ossa illii and the upper part of the sacrum; and the _small pelvis_, or basin, which is enclosed between the lower part of the sacrum and coccygis behind, and the ossa ischii and ossa pubes in front. The basin is nearly cylindrical, larger in the middle, and curved towards the front. _The Straits of the Pelvis._--The bones of the Pelvis, it will be seen, form a kind of broad ring, or cylinder, particularly in the basin; and the straits are two passages, one by which the child passes into the basin from the upper Pelvis, and the other by which it passes out from the basin into the world.