As this concise work is intended for those who are entering upon the practical part of Midwifery, and who consequently must be supposed to have made themselves acquainted with the structure of the parts concerned in parturition, it does not appear necessary to dwell long upon their anatomy. The bony structure of the pelvis will, therefore, be alone described, and that very briefly. When we consider that this part contains the internal organs of generation; that it gives attachment to the external; that it affords a natural impediment to the passage of the child during labour; and that, from disease, its shape may become so altered as to present difficulties to the completion of that process insurmountable by nature alone; the importance of a thorough knowledge of the anatomy of the pelvis, before attempts are made to give assistance at the time of childbirth, will be sufficiently apparent.
The PELVIS is that portion of the skeleton situated at the lower part of the spine and above the thigh-bones: with the former it is firmly connected by cartilage and ligament; and with the latter, by means of the acetabular into which these bones are received,
The adult pelvis consists of four bones: two ossa innominata, forming the anterior and lateral parts; the sacrum, and the os coccygis, forming the posterior part.
In the foetus, and in early childhood, the os INNOMINATUM is distinctly divided into three portions: the ilium forming the upper, and by far the largest part; the ischium, the lower; and the pubis, the fore part. They all unite in forming the acetabulum, a cavity which receives the head of the thigh-bone. By this large mass of bone being thus, in the foetus, composed of three portions loosely connected together by cartilage, a certain degree of overlapping is allowed, by which parturition is somewhat assisted.
The SACRUM is a triangular bone situated at the posterior part of the pelvis, firmly connected to the spine above, to the os innominatum on either side, and to the os coccygis below. Internally it is concave: and this concavity is obstetrically termed the hollow of the sacrum; from the foramina at the sides of which, nerves of considerable size are passing out; and the pressure which these nerves undergo is the cause why parturient women so frequently complain of "cramps" in the thighs. By its union with the last lumbar vertebra, a protuberance is formed, called the promontory of the sacrum.
The os coccygis is that small bone attached to the extremity of the sacrum, to which it is firmly connected; but in such a manner as to allow of a considerable degree of motion when pressed upon by the head of the child, and thus to enlarge the outlet of the pelvis. For this purpose we find the ends of both bones tipped with cartilage, and covered with synovial membrane; and there is a perfect capsular ligament to the joint. This joint sometimes yields with difficulty to the pressure of the child, whereby considerable pain and inconvenience is experienced by the patient.
The OSSA INNOMINATA are united together before, and to the sacrum behind, in a very strong and effectual manner. But, although the ossa innominate are united at their upper pan, we find they afterwards recede very considerably from each other, passing down wards and backwards; and this separation, or divergence, forms an arch, of great importance in midwifery, which is called the Pubic Arch.
The PELVIS being formed by the junction of these bones, is divided into two parts: the great or false, and the little or true, pelvis; the former comprehending that portion situated above the linea-ilio-pectinea, which is a prominent line, commencing from the upper part of the junction of the ilium with the sacrum, and extending all round to the corresponding part on the opposite side; the latter comprehending the part below it.
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From Charles Waller
Elements of Practical Midwifery: Or, Companion to the Lying-in Room, 1829
