PLATE VIII.
Section of the Pelvis, to show the shape and connection of those parts not distinctly visible in the full view. The section is made down the middle of the back bone, and through the symphysis pubes, in front. The letters correspond with those in Plate VII.
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.
In Plate VIII. the line marked ┼ is the antero posterior diameter of the upper strait, through which the child first passes, called also the brim, or entrance to the Pelvis. The line marked ╬ is the diameter of the lower strait, through which the child passes into the world, called also the outlet of the Pelvis. In Plate VII. the line marked ┼ crosses the upper strait, or brim of the Pelvis.
The diameters of the Pelvis are the distances between the prominent points of each strait, and are four in number for each, those for the upper strait being represented below.
PLATE IX.
Diameters of the Upper Strait.
A B, which extends from the most prominent point of the Sacrum, to the top of the Symphysis pubes, is called the antero posterior diameter, or that from before to behind.-C D, and E F, are called the two oblique diameters; they extend from each sacro iliac symphysis, to the most prominent point of the Os Ilium on the opposite side.-G H, is called the Transverse, or bis iliac diameter, it crosses the Pelvis nearly from one hip joint to the other.
The Sacro Antero posterior diameter measures four inches. The two oblique diameters four inches and a half each. The bis iliac diameter measures five inches.
(By comparing this with Plate VII. the various points will be still more apparent.)
The inferior strait has also four diameters, represented in Plate X.
Plate IX.
Diameters of the Upper Strait.
PLATE X.
The Bones of the Pelvis viewed from below, looking through the inferior strait, to show its diameters.
A B, which extends from the end of the Coccygis to the lower part of the Symphysis Pubis, is called the antero posterior diameter; it measures four inches, like that of the upper strait, but is increased a little by the bending back of the Coccygis.-C D, and E F, are the two oblique diameters, also corresponding to those in the upper strait; they measure four inches, but are increased a little by the giving way of the soft parts.-G H, is the transverse, or bis-ischiatic diameter; it measures four inches.
Plate X.
The Bones of the Pelvis viewed from below, looking through the inferior strait, to show its diameters.
It will thus be seen that the diameters only average from four to five inches, but it must be remembered that the soft parts, and even one of the bones, very readily give way, and thus they are slightly increased.
When we come to describe the form and size of the fotal child's head, it will be found that its diameters correspond very nearly with those of the pelvic straits through which it has to pass, so that ordinarily labor presents no serious difficulty. If the head be larger than natural, from any cause, or if the Pelvis be too small, or deformed, this mutual adaptation does not exist, and delivery of course becomes difficult, or dangerous, and sometimes impossible. The only obstacle therefore, which can seriously impede the expulsion of the fotus, or prevent it altogether, is this want of conformity, in size and shape, between its head and the bones of the Pelvis. The soft parts may retard labor considerably, by being contracted or rigid, but can generally be made to give way, either by the efforts of nature or by manual assistance; and the fotal head can be reduced in size if necessary; but insufficient size, or faulty form, in the bones, is irremediable.
The various causes which produce deformity, or imperfect development, in the Pelvis, and unnatural growth of the child's head, will be stated in a subsequent section. For the present, we have only to do with both in the normal state.
The importance of an accurate knowledge of the structure of the Pelvis, and of the changes which may be induced in it, will now be obvious; neither the theory nor the practice of Midwifery can in fact be understood without such knowledge. It is also frequently of the first importance to know, previous to marriage, whether the pelvis of a young person is so formed that delivery can be safely effected! Inattention to this has sacrificed the lives of many, and caused others to live for years suffering and helpless. In another place we shall give some plain rules and directions by which this important point may be determined.
The floor of the Pelvis.-The soft parts at the bottom of the basin of the Pelvis, consisting of the perineum and various muscles, are called the floor of the Pelvis-the only passage through which is by the Vulva, or mouth of the Vagina. As the head of the child descends to the bottom of the basin, it presses upon this floor, and gradually distends it, until the Vulva is sufficiently enlarged. This delay is advantageous, for if the passage was always large enough, or increased in size without any difficulty, the child would pass too suddenly, and much mischief might often result from its sudden expulsion-such as pulling down of the womb, flooding, and the falling of the child upon the ground.
Direction of the passage of the Pelvis.-In most of the lower animals the passage of the Pelvis is straight, and on a line with the body, the two straits being opposite each other, which makes delivery much more easy with them. Even in the negroes, and other inferior races, the passage is much straighter than in the whites. The more perfect the organization therefore, the more difficult is parturition; and the more imperfect or simple the organization, the more easy is parturition. The dotted line in Plate XI. shows the direction of the passage of the Pelvis, in the human female, to be a curve, so that the child has to move, during its passage, in a circle.
PLATE XI.
The axis, or direction, of the upper strait is denoted by the line A, that of the lower strait by the line B, and that of the Vulva by the line C. The force of expulsion tending to push the child in each direction, it has to traverse a path intermediate with them all, or compounded of them all, not being able to move in either alone. This aggregate...
