Functions and Movements of the Pelvis.
The pelvis of woman, says Pajot, plays an indispensable part in the ac complishment of two important functions, generation and locomotion. It serves moreover to support, contain, and protect several essential or gans.
The pelvis supports the trunk and upper extremities; therefore it is formed of large, resisting bones, so placed as to make a complete ring. This ring resists the strain by the aid of two essential conditions: the strength of the bony elements which form it, and the direction in which it is interposed between the vertebral column and the lower extremities.
The strength of the bone is especially remarkable in the sacrum, in that portion of the ossa innominata which lies between the articular facet and the cotyloid cavity, and the portion which foims the base of the ischium.
The pelvis is placed between the vertebral column, and the inferior ex tremities, so as to form a very oblique ring. This ring receives the weight of the trunk on its highest point, and it is supported by the femurs at its anterior and lateral parts. Now this ring may be divided into two nearly equal parts, or two arcs. The superior arc sustains, at its centre, the vertebral column; it ends at the cotyloid cavities, and the femurs. The centre of the inferior arc is the pubic symphysis; it also ends at the cotyloid cavities where it joins the superior arc.
The superior half forms an arch which completes and strengthens the inferior half, which is shaped like an inverted arch. (Dubois and Pajot).
The pelvis protects the viscera, and in its interior the development of the organs and of the fcetus takes place.
The movements of the pelvis are very limited on account of the mode of union of its various pieces. Yet it has movements of flexion, of exten sion, of lateral inclination, of rotation about a vertical axis, and even of circumduction (Tarnier). Movements of the bones among themselves only exitt in the sacro-cocygeal articulation. If, during pregnancy, the swelling and imbibition of the interarticular cartilages separate the bones a little, it is not enough to justify the opinion of the ancients, who thought that the bones could move so as to cause a dilation of the pelvis.
In the pubic symphysis these phenomena are the most pronounced, but it is only in pathological cases, called relaxation of the symphyses, that these movements become appreciable. Matthews Duncan has made a study of the articulations of the pelvis during confinement. We will con fine ourselves to mentioning this work, to which we will return later.
Soft Parts of the Pelvis.
The pelvis is covered on the inside and outside by soft parts. The first of these have a direct relation to pregnancy and confinement; the others on the contrary, can only be called accessories. We will pass rapidly over these4ast, before making a careful study of the former.
Soft Parts of the External Surface.
Those which are posterior are only of a secondary interest. With the ex-' ception of the glutei-maximi muscles, which unite to form a part of the perineal floor, none of these parts have any direct relation to the ob ject of our research. It is not the same with those which are situated anteriorly. These may be divided into two classes: those which belong essentially to the pelvis, and which form the region of the external genital organs; those which form only accessorily a part of the pelvis, and which close the great notch in the anterior part of the pelvis. We will first des cribe the abdominal walls.
I. Abdominal Walls.
Only the lower third of the abdominal wall helps to close the pelvis in front; that is, only the hypogastric region. We must not, however, for get the part which the abdominal walls play in the act of parturition: we will, therefore, say a few words about that portion which forms the abdo men. Following Richet, we distinguish four walls 1st. The superior wall, formed by the diaphragmatic region.
2d. The posterior wall formed by the lumbar portion of the great spinal region.