THE PELVIS
The Pelvis is composed of four bones. The two Ossa Innominata, which bound it in front and at the sides, and the Sacrum and Coccyx, which complete it behind.
THE OS INNOMINATUM
The Os Innominatum, so called from bearing no resemblance to any known object, is a large irregular-shaped bone, which, with its fellow of the opposite side, forms the sides and anterior wall of the pelvic cavity. In young subjects, it consists of three separate parts, which meet and form the large cup-like cavity, situated near the middle of the outer side of the bone; and, although in the adult these have become united, it is usual to describe the bone as divisible into three portions, the ilium, the ischium, and the pubes.
The ilium is the superior broad and expanded portion which runs upwards from the upper and back part of the acetabulum, and forms the prominence of the hip.
The ischium is the inferior and strongest portion of the bone; it proceeds downwards from the acetabulum, expands into a large tuberosity, and then curving upwards, forms with the descending ramus of the pubes a large aperture, the obturator foramen.
The pubes is that portion which runs horizontally inwards from the inner side of the acetabulum for about two inches, then makes a sudden bend, and descends to the same extent: it forms the front of the pelvis, and supports the external organs of generation.
The Ilium presents for examination two surfaces, an external and an internal, a crest, and two borders, an anterior and a posterior.
External Surface or Dorsum of the Ilium . The back part of this surface is directed backwards, downwards, and outwards; its front part forwards, downwards and outwards. It is smooth, convex in front, deeply concave behind; bounded above by the crest, below by the upper border of the acetabulum, in front and behind by the anterior and posterior borders. This surface is crossed in an arched direction by three semicircular lines, the superior, middle, and inferior curved lines. The superior curved line, the shortest of the three, commences at the crest, about two inches hi front of its posterior extremity; it is at first distinctly marked, but as it passes downwards and outwards to the back part of the great sacro-sciatic notch, where it terminates, it becomes less marked, and is often altogether lost. The rough surface included between this line and the crest, affords attachment to part of the Gluteus maximus above, a few fibres of the Pyriformis below. The middle curved line, the longest of the three, commences at the crest, about an inch behind its anterior extremity, and, taking a curved direction downwards and backwards, terminates at the upper part of the great sacro-sciatic notch. The space between the middle, the superior curved lines, and the crest, is concave, and affords attachment to the Gluteus medius muscle. Near the central part of this line may often be observed the orifice df a nutritious foramen. The inferior curved line, the least distinct of the three, commences in front at the upper part of the anterior inferior spinous process, and taking a curved direction backwards and downwards, terminates at the anterior part of the great sacro-sciatic notch. The surface of bone included between the middle and inferior curved lines, is concave from above downwards, convex from before backwards, and affords attachment to the Gluteus minimus muscle. Beneath the inferior curved line, and corresponding to the upper part of the acetabulum, is a smooth eminence (sometimes a depression), io which is attached the reflected tendon of the Rectus femoris muscle.
Os Innominatum, External Surface
The Internal Surface of the ilium is bounded above by the crest, below by a prominent line, the linea-ileo pectinea, and before and behind by the anterior and posterior borders. It presents anteriorly a large smooth concave surface called the internal iliac fossa, or venter of the ilium; it lodges the Iliacus muscle, and presents at its lower part the orifice of a nutritious canal. Behind the iliac fossa is a rough surface, divided into two portions, a superior and an inferior. The inferior, or auricular portion, so called from its resemblance to the external ear, is coated with cartilage in the recent state, and articulates with a similar shaped surface on the side of the sacrum. The superior portion is concave and rough for the attachment of the posterior sacro-iliac ligaments.
Os Innominatum, Internal Surface
The crest of the ilium is convex in its general outline and sinuously curved, being bent inwards anteriorly, outwards posteriorly. It is longer in the female than in the male, very thick behind, and thinner at the centre than at the extremities. It terminates at either end in a prominent eminence, the anterior superior, and posterior superior spinoua process. The surface of the crest is broad, and divided into an external lip, an internal lip, and an intermediate space. To the external lip is attached the Tensor vaginae femoris, Obliquus externus abdominis, and Latissimus dorsi, and by its whole length the fascia lata; to the interspace between the lips, the Internal oblique; to the internal lip, the Transversalis, Quadratus lumborum, and Erector spinae.
The anterior border of the ilium is concave. It presents two projections separated by a notch. Of these, the uppermost, formed by the junction of the crest and anterior border, is called the anterior superior spinous process of the ilium, the outer border of which gives attachment to the fascia lata, and the origin of the Tensor vaginae femoris, its inner border, to the Iliacus interims, whilst its extremity affords attachment to Foupart's ligament and the origin of the Sartorius. Beneath this eminence, is a notch which gives attachment to the Sartorius muscle, and across which passes the external cutaneous nerve. Below the notch is the anterior inferior spinous process, which terminates in the upper lip of the acetabulum; it gives attachment to the straight tendon of the Rectus femoris muscle. On the inner side of the anterior inferior spinous process, is a broad shallow groove, over which passes the Iliacus muscle. The posterior border, shorter than the anterior, also presents two projections separated by a notch, the posterior superior, and the posterior inferior spinous processes. The former corresponds with that portion of the posterior surface of the ilium, which serves for the attachment of the sacro-iliac ligaments, the latter, to the auricular portion which articulates with the sacrum. Below the posterior inferior spinous process, is a deep notch, the great sacro-sciatic.
The Ischium forms the inferior and posterior part of the os innominatum. It is divisible into a thick and solid portion, the body, and a thin ascending part, the ramus. The body, somewhat triangular in form, presents three surfaces, an external, internal, and posterior, and three borders. The external surface corresponds to that portion of the acetabulum formed by the ischium; it is smooth and concave above, and forms a little more than two-fifths of that cavity; its outer margin is bounded by a prominent rim or lip, to which the cotyloid-fibro-cartilage is attached. Below the acetabulum, between it and the tuberosity, is a deep groove, along which the tendon of the Obturator externus muscle runs, as it passes outwards to be inserted into the digital fossa of the femur. The internal surface is smooth, concave, and forms the lateral boundary of the true pelvic cavity; it is broad above, and separated from the venter of the ilium by the linea-ileo-pectinea, narrow below, its posterior border being encroached upon a little below its centre, by the spine of the ischium, above and below which are the greater and lesser sacro-sciatic notches; in front it presents a sharp margin, which forms the outer boundary of the obturator foramen. This surface is perforated by two or three large vascular foramina, and affords attachment to part of the Obturator internus muscle.
The posterior surface is quadrilateral in form, broad and smooth above, narrow below where it becomes continuous with the tuberosity; it is limited in front by the margin of the acetabulum, behind by the front part of the great sacro-sciatic notch. This surface supports the Pyriformis, the two Gemelli, and the Obturator internus muscles, in their passage outwards to the great trochanter. The body of the ischium presents three borders, posterior, inferior, and internal. The posterior border presents, a little below the centre, a thin and pointed triangular eminence, the spine of the ischium. more or less elongated in different subjects. Its external surface gives attachment to the Gemellus superior, its internal surface to the Coccygeus and Levator ani, whilst to the pointed extremity is connected the lesser sacro-sciatic ligament. Above the spine is a notch of large size, the great sacro-sciatic, converted into a foramen by the lesser sacro-sciatic ligament; it transmits the Pyriformis muscle, the gluteal vessels and nerve
passing out above this muscle, the sciatic, and internal pudic vessels and nerve, and a small nerve to the Obturator internus muscle below it. Below the spine is a smaller notch, the lesser sacro-sciatic; it is smooth, coated with cartilage in the recent state, the surface of which presents numerous markings corresponding to the subdivisions of the tendon of the Obturator internus which winds over it. It is converted into a foramen by the sacro-sciatic ligaments, and transmits the tendon of the Obturator internus, the nerve which supplies this muscle, and the pudic vessels and nerve. The inferior border is thick and broad: at its point of junction with the posterior, is a large rough eminence upon which the body rests in sitting; it is called the tuberosity of the ischium. The internal border is thin, and forms the outer circumference of the obturator foramen.
The tuberosity, situated at the junction of the posterior and inferior borders, presents for examination an external lip, an internal lip, and an intermediate space. The external lip gives attachment to the Quadratus femoris and part of the Adductor magnus muscles. The inner lip is bounded by a sharp ridge for the attachment of a falciform prolongation of the great sacro-sciatic ligament, presents a groove on the inner side of this for the lodgment of the internal pudic vessels and nerve, and more anteriorly has attached the Transversus perinei, Erector penis, and Compressor urethrae muscles. The intermediate surface presents four distinct impressions. Two of these seen at the front part of the tuberosity are rough, elongated, and separated from each other by a prominent ridge; the outer one gives attachment to the Adductor magnus, the inner one to the great sacro-sciatic ligament. Two situated at the back part are smooth, larger in size and separated by an oblique ridge: from the upper and outer arises the Semi-membranosus; from the lower and inner, the Biceps and Semi-tendinosus. The most superior part of the tuberosity gives attachment to the Gemellus inferior.
The ramus is the thin flattened part of the ischium, which ascends from the tuberosity upwards and inwards, and joins the ramus of the pubes, their point of junction being indicated in the adult by a rough eminence. Its outer surface is rough for the attachment of the Obturator externus muscle. Its inner surface forms part of the anterior wall ef the pelvis. Its inner border is thick, rough, slightly everted, forms part of the outlet of the pelvis, and serves for the attachment of the crus-penis. Its outer border is thin and sharp, and forms part of the inner margin of the obturator foramen.
The Pubes forms the anterior part of the os innominatum; it is divisible into a horizontal ramus or body, and a perpendicular ramus.
The body, or horizontal ramus, presents for examination two extremities, an outer and an inner, and four surfaces. The outer extremity, the thickest part of the bone, forms one-fifth of the cavity of the acetabulum: it presents above, a rough eminence, the ilio-pectineal, which serves to indicate the point of junction of the ilium and pubes. The inner extremity of the body of the bone is the symphysis; it is oval, covered by eight or nine transverse ridges, or a series of nipple-like processes arranged in rows, separated by grooves; they serve for the attachment of the interarticular fibro-cartilage, placed between it and the opposite bone. Its upper surface, triangular in form, wider externally than internally, is bounded behind by a sharp ridge, the pectineal line, or linea-ilio-pectinea, which, running outwards, marks the brim of the true pelvis. The surface of bone in front of the pubic portion of the linea-ilio-pectinea, serves for the attachment of the Pectineus muscle. This ridge terminates internally at a tubercle, which projects forwards, and is called the spine of the pubes. The portion of bone included between the spine and inner extremity of the pubes is called the crest; it serves for the attachment of the Rectus, Pyrami-dalis, and conjoined tendon of the Internal oblique and Transversalis. The point of junction of the crest with the symphysis is called the angle of the pubes. The inferior surface presents externally a broad and deep oblique groove, for the passage of the obturator vessels and nerve; and internally a sharp margin, which forms part of the circumference of the obturator foramen. Its external surface is flat and compressed, and serves for the attachment of muscles. Its internal surface, convex from above downwards, concave from side to side, is smooth, and forms part of the anterior wall of the pelvis. The descending ramus of the pubes passes outwards and downwards, becoming thinner and narrower as it descends, and joins with the ramus of the ischium. Its external surface is rough, for the attachment of muscles. Its inner surface is smooth. Its inner border is thick, rough, and everted, especially in females. In the male it serves for the attachment of the crus penis. Its outer border forms part of the circumference of the obturator foramen.
The cotyloid cavity or acetabulum, is a deep cup-shaped hemispherical depression; formed internally by the pubes, above by the ilium, behind and below by the ischium, a little less than two-fifths being formed by the ilium, a little more than two-fifths by the ischium, and the remaining fifth by the pubes. It is bounded by a prominent uneven rim, which is thick and strong above, and serves for the attachment of a fibre-cartilaginous structure, which contracts its orifice and deepens the surface for articulation. It presents on its inner side a deep notch, the cotyloid notch, which transmits the nutrient vessels into the interior of the joint, and is continuous with a deep circular depression at the bottom of the cavity: this depression is perforated by numerous apertures, lodges a mass of fat, and its margins serve for the attachment of the ligamentum teres. The notch is converted, in the natural state, into a foramen by a dense ligamentous band which passes across it. Through this foramen the nutrient vessels and nerves enter the joint.
The obturator or thyroid foramen is a large aperture, situated between the ischium and pubes. In the niale it is large, of an oval form, its longest diameter being obliquely from above downwards; in the female smaller, and more triangular. It is bounded by a thin uneven margin, to which a strong membrane is attached; and presents at its upper and outer part a deep groove, which runs from the pelvis obliquely forwards, inwards, and downwards. It is converted into a foramen by the obturator membrane, and transmits the obturator vessels and nerve.
Development of Os Innominatum
Structure. This bone consists of much cancellous tissue, especially where it is thick, enclosed between two layers of thick and dense compact tissue. In the thinner parts of the bone, as at the bottom of the acetabulum, and centre of the iliac fossa, it is usually semi-transparent, and composed entirely of compact tissue.
Development (6g. 71). By eight centres: three primary—one for the ilium, one for the ischium, and one for the pubes; an&Jive secondary—one for the crest of the ilium its whole length, one for the anterior inferior spinous process (said to occur more frequently in the male than the female), one for the tuberosity of the ischium, one for the symphysis pubis (more frequent in the female than the male), and one for the Y-shaped piece at the bottom of the acetabulum. These various centres appear in the following order: First, in the ilium, at the lower part of the bone, immediately above the sciatic notch, at about the same period that the development of the vertebrae commences. Secondly, in the body of the ischium, at about the third month of foetal life. Thirdly, in the body of the pubes, between the fourth and fifth months. At birth, these centres are quite separate; the crest, the bottom of the acetabulum, and the rami of the ischium and pubes, being still cartilaginous. At about the sixth year, the rami of the pubes and ischium are almost completely ossified. About the thirteenth or fourteenth year, the three divisions of the bone have extended their growth into the bottom of the acetabulum, being separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification. The ilium and ischium then become joined, and lastly the pubes, through the intervention of the portion above mentioned. At about the age of puberty, ossific matter appears in each of the remaining portions, and they become joined to the rest of the bone about the twenty-fifth year.
Articulations. With its fellow of the opposite side, the sacrum and femur.
Attachment of Muscles. Ilium . To the outer lip of the crest, the Tensor vaginas femoris, Obliquus externus abdominis, and Latissimus dorsi; to the internal lip, the Transversalis, Quadratus lumborum, and Erector spinae; to the interspace between the lips, the Obliquus internus. To the outer surface of the ilium, the Gluteus maximus, Gluteus medius, Gluteus minimus, reflected tendon of Rectus, portion of Pyriformis; to the internal surface, the Iliacus; to the anterior border, the Sartorius and straight tendon of the Rectus. To the ischium. Its outer surface, the Obturator externus; internal surface, Obturator internus and Levator ani. To the spine. The Gemellus superior, Levator ani, and Coccygeus. To the tuberosity, the Biceps, Semi-tendinosus, Semi-membranosus, Quadratus femoris, Adductor magnus, Gemellus inferior, Transversus perinaei, Erector penis. To the pubis, the Obliquus externus, Obliquus internus, Transversalis, Rectus, Pyramida-lis, Psoas parvus, Pectineus, Adductor longus, Adductor brevis, Gracilis, Obturator externus and internus, Levator ani, Compressor urethrae, and occasionally a few fibres of the Accelerator urinae.
THE PELVIS
The pelvis is stronger and more massively constructed than either of the other osseous cavities already considered; it is connected to the lower end of the spine, which it supports, and transmits its weight to the lower extremities, upon which it rests. It is composed of four bones—the two ossa innominata, which bound it on either side and in front; and the sacrum and coccyx, which complete it behind.
The pelvis is divided by a prominent line, the linea ileo pectinea, into a false and true pelvis.
The false pelvis is all that expanded portion of the pelvic cavity which is situated above the linea ileo pectinea. It is bounded on each side by the ossa ilii; in front it is incomplete, presenting a wide interval between the anterior superior spinous processes of the ilia on either side, filled up in the recent state by the parietes of the abdomen; behind, in the middle line, is a deep notch. This broad shallow cavity is admirably adapted to support the intestines, and to transmit part of their weight to the anterior wall of the abdomen.
The true pelvis is all that part of the pelvic cavity which is situated beneath the linea ileo pectinea. It is smaller than the false pelvis, but its walls are more perfect. For convenience of description, it may be divided into a superior circumference or inlet, an inferior circumference or outlet, and a cavity.
The superior circumference forms the margin or brim of the pelvis, the included space being called the inlet. It is formed by the linea ileo pectinea, completed in front by the spine and crest of the pubes, and behind by the anterior margin of the base of the sacrum and sacro-vertebral angle.
The inlet of the pelvis is somewhat cordate in form, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forwards of the promontory of the sacrum. It has three principal diameters: antero-poste-rior (sacro-pubic), transverse, and oblique. The antero-posterior extends from the sacro-vertebral angle to the symphysis pubis; its average measurement is four inches. The transverse extends across the greatest width of the pelvis, from the middle of the brim on one side, to the same point on the opposite; its average measurement is five inches. The oblique extends from the margin of the pelvis corresponding to the ileo pectineal eminence on one side, to the sacro-iliac symphysis on the opposite side; its average measurement is also five inches.
The cavity of the true pelvis is bounded in front by the symphysis pubis; behind, by the concavity of the sacrum and coccyx, which, curving forwards above and below, contracts the inlet and outlet of the canal; and laterally it is bounded by a broad, smooth, quadrangular plate of bone, corresponding to the inner surface of the body of the ischium. This cavity is shallow in front, measuring at the symphysis an inch and a half in depth, three inches and a half in the middle, and four inches and a half posteriorly. From this description, it will be seen that the cavity of the pelvis is a short, curved canal, considerably deeper on its posterior than on its anterior wall, and broader in the middle than at either extremity, from the projection forwards of the sacro-coccygeal column above and below. This cavity contains, in the recent subject, the rectum, bladder, and part of the organs of generation. The rectum is placed at the back of the pelvis, and corresponds to the curve of the sacro-coccygeal column, the bladder in front, behind the symphysis pubis. In the female, the uterus and vagina occupy the interval between these parts.
The lower circumference of the pelvis is very irregular, and forms what is called the outlet. It is bounded by three prominent eminences: one posterior, formed by the point of the coccyx; and one on each side, the tuberosities of the ischia. These eminences are separated by three notches; one in front, the pubic arch, formed by the convergence of the rami of the ischia and pubes on each side. The other notches, one on each side, are formed by the sacrum and coccyx behind, the ischium in front, and the ilium above: these are called the greater and lesser sacro-sciatic notches; in the natural state they are converted into foramina by the lesser and greater sacro-sciatic ligaments.
The diameters of the outlet of the pelvis are two, antero-posterior and transverse. The antero-posterior extends from the tip of the coccyx to the lower part of the symphysis pubis; and the transverse from the posterior part of one ischiatic tuberosity, to the same point on the opposite side: the average measurement of both is four inches. The antero-posterior diameter varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of this bone.
Position of the Pelvis. In the erect posture, the pelvis is placed obliquely with regard to the trunk of the body; the pelvic surface of the symphysis pubis looking upwards and backwards, the concavity of the sacrum and coccyx looking downwards and forwards. The base of the sacrum, in well-formed female bodies, being nearly four inches above the upper border of the symphysis pubis, and the apex of the coccyx a little more than half an inch above its lower border. This obliquity is much greater in the foetus, and at an early period of life, than in the adult.
Axes of the Pelvis. The plane of the inlet of the true pelvis will be represented by a line drawn from the base of the sacrum to the upper margin of the symphysis pubis. A line carried at right angles with this at its middle, would correspond at one extremity with the umbilicus, and by the other with the middle of the coccyx; the axis of the inlet is therefore directed downwards and backwards. The axis of the outlet produced upwards, would touch the base of the sacrum; and is therefore directed downwards and forwards. The axis of the cavity is curved like the cavity itself: this curve corresponds to the concavity of the sacrum and coccyx, the extremities being indicated by the central points of the inlet and outlet.
Differences between the Male and Female Pelvis. In the male, the bones are heavier, stronger, and more solid, and the muscular impressions and eminences on their surfaces more strongly marked. It is altogether more massive in its general form; its cavity is deeper and narrower, and its apertures small. In the female, the bones are lighter and more delicate, the muscular impressions on its surface only slightly marked, and the pelvis generally is less massive in structure. The iliac fossae are large, and the ilia widely expanded; hence the great prominence of the hips. The cavity is shallow, but capacious, being very broad both in the antero-posterior and transverse diameters; the inlet and outlet are also large. The obturator foramen is triangular; the tuberosities of the ischia are widely separated; the sacrum is wider and less curved; the symphysis pubis not so deep; and the arch of the pubis is greater, and its edges more everted.
In the foetus, and for several years after birth, the cavity of the pelvis is small; the viscera peculiar to this cavity in the adult, being situated in the lower part of the abdomen.
