Introduction to the Pelvis and Perineum; Anal Triangle

Gross Anatomy


Introduction to the Pelvis and Perineum; Anal Triangle


Anatomy Tables for Today's Topic

Bones of the Pelvis and Perineum
Joints of the Pelvis
Viscera
Muscles of the Anal Triangle
Nerves of the Perineum
Arteries of the Perineum
Veins of the Perineum
Topographic Anatomy of the Perineum
Lymphatics of the Perineum

Bones of the Pelvis and Perineum

Bone Structure Description Notes
os coxae one of three bones that form the pelvis paired; the os coxae forms the lateral part of the pelvis; it is formed by three fused bones: ischium, ilium & pubis; also known as the innominate bone
acetabulum a cup-shaped depression in the lateral surface of the os coxae bone acetabulum means vinegar cup; it is the socket for the head of the femur; it is formed by the: ilium (1/5), ischium (2/5) and pubis (2/5); the acetabular fossa lies in the floor of the acetabulum
acetabular notch a notch in the inferior margin of the acetabulum it is spanned by the transverse acetabular ligament; the acetabular br. of the obturator a. enters the hip joint by passing through the acetabular notch
acetabular fossa a roughened depression in the center of the acetabulum the ligament of the head of the femur occupies the acetabular fossa
lunate surface of the acetabulum the smooth articular surface of the acetabulum the lunate surface surrounds the acetabular fossa and the acetabular notch
obturator foramen a large foramen formed by the pubic and ischial rami obturator means to occlude or stop up, a reference to the fact that the obturator membrane closes the obturator foramen almost completely; a site of attachment for the obturator externus m. and the obturator internus m.
pubis an angulated bone the forms the anterior part of the pelvis one of three bones that form the os coxae: ilium, ischium, pubis; its body forms 1/5 of the acetabulum; its symphyseal surface unites with the pubis of the opposite side to form the pubic symphysis; the superior and inferior pubic rami participate in the formation of the obturator foramen
body superolateral portion of the pubis the body of the pubis forms about 1/5 of the acetabulum
pubic crest ridge on the superior border of the superior ramus attachment of rectus abdominis & pyramidalis mm.
pubic tubercle process at the lateral end of pubic crest attachment point of the medial end of the inguinal ligament
superior ramus superior "limb" that passes medially from the body of the pubis articulates with the superior ramus of the opposite side at the pubic symphysis
pecten ridge on superior surface of the superior pubic ramus attachment point of the pectineal ligament
inferior ramus inferior "limb" that passes inferolaterally from the pubic symphysis articulates with the ischial ramus to form the ischiopubic ramus; attachment site for the root of the penis (clitoris)
obturator groove groove on the inferior surface of the superior pubic ramus marks the area of passage of the obturator vessels and n. in the obturator canal
ischium   the "V"- shaped bone that forms the posteroinferior part of the pelvis one of the three bones that form the os coxae: ilium, ischium, pubis
  ischial ramus the limb of the ischium that passes anteriorly and superomedially toward the pubis it articulates with the inferior ramus of the pubis
body the part of the ischium that participates in the formation of the acetabulum it articulates with the ilium and the pubis at the acetabulum; the body of the ischium forms 2/5 of the acetabulum
ischial tuberosity the roughened projection that protrudes posteroinferiorly from the body of the ischium it is the site of attachment of the sacrotuberous ligament; it is the site of origin of the inferior gemellus m., quadratus femoris m. and the hamstring mm. (semitendinosus, semimembranosus, long head of biceps femoris, ischiocondylar portion of the adductor magnus)
lesser sciatic notch the notch located between the ischial tuberosity and the ischial spine the lesser sciatic notch is converted to the lesser sciatic foramen by the sacrospinous ligament and the sacrotuberous ligament
ischial spine the spine that arises just superior to the lesser sciatic notch it is the site of attachment of the sacrospinous ligament and the site of origin of the superior gemellus m.
ilium fan-shaped bone that forms the lateral prominence of the pelvis one of three bones that form the os coxae: ilium, ischium, pubis
body the portion of the ilium that participates in the formation of the acetabulum the body of the ilium forms 2/5 of the acetabulum
iliac crest arching superior edge the ilium that forms the rim of the "fan" attachment for abdominal wall muscles
iliac tubercle roughened area along the outer edge of the iliac crest
anterior superior iliac spine spine at the anterior end of the iliac crest lateral attachment of the inguinal ligament
posterior superior iliac spine spine at the posterior end of the iliac crest position marked by a dimpling of the skin
arcuate line ridge running from anteroinferior to posterosuperior on the inner surface of the ilium inferior boundary of the iliac fossa; marks the plane of transition from abdominal cavity to pelvic cavity
sacrum   a triangular bone that is the posterior skeletal element forming the pelvis it is formed by 5 fused vertebrae; the sacrum and two os coxae bones form the pelvis
base the superior part of the sacrum the base of the sacrum includes the articular surface for the fifth lumbar vertebra and the superior portion of the two ala
promontory a projection of the superior part of the sacrum in an anterior direction the body of the fifth lumbar vertebra sits on the sacral promontory and articulates with it through a symphysis
ala the lateral portion of the sacrum paired; it projects laterally from the body of the sacrum; it represents the fused costal and transverse processes of the first sacral vertebra
anterior sacral foramina an opening in the anterior surface of the sacrum there are four pairs; each transmits the ventral primary ramus of the respective sacral spinal nerve; branches of the lateral sacral aa. Enter the sacral canal through these openings
posterior sacral foramina an opening in the posterior surface of the sacrum there are four pairs; each transmits the dorsal primary ramus of the respective sacral spinal nerve
sacral canal the opening in the center of the sacrum it is the continuation of the vertebral canal at sacral vertebral levels
sacral hiatus an opening in the posterior surface of the sacrum in the midline it is a normal feature that results from the failure of fusion of the laminae of the fifth sacral segment (and sometimes the fourth) during development
articular surface the roughened area located on the lateral surface of the sacrum this surface articulates with the ilium in the sacroiliac articulation
body the central portion of the sacrum the body is equivalent to the bodies of the other vertebra
base the superior surface of the sacrum the base of the sacrum articulates with the fifth lumbar vertebra through an intervertebral disk
coccyx   the most inferior portion of the vertebral column the coccyx results from the fusion of the four coccygeal vertebrae; it may be a single bone or the first coccygeal vertebra may be separated from the other three; it articulates with the fifth sacral segment; coccygeal vertebrae are reduced in complexity, having no pedicles, laminae or spines

Joints of the Pelvis

Joint or ligament Description Notes
iliolumbar ligament a ligament that connects the transverse process of the L5 vertebra to the iliac crest the iliolumbar ligament stabilizes the lumbosacral joint
pubic symphysis the midline joint uniting the superior rami of the two pubic bones a symphysis; a fibrocartilage interpubic disk unites the bones; the subpub angle in the female is greater than the subpubic angle in the male
sacroiliac joint the articulation between the ala of the sacrum and the auricular surface of the ilium a synovial joint; the fibrous articular capsule is thickened dorsally and ventrally to form the sacroiliac ligaments; because of the interlocking nature of the joint surfaces and the strong sacroiliac ligaments, only limited movement is permitted at the sacroiliac joint
sacrospinous ligament the ligament that connects the ischial spine to the lateral surface of the sacrum and coccyx together with the sacrotuberous ligament, it converts the greater and lesser sciatic notches into greater and lesser sciatic foramina
sacrotuberous ligament the ligament that connects the ischial tuberosity to the lateral surface of the sacrum and coccyx together with sacrospinous ligament, it converts the greater and lesser sciatic notches into greater and lesser sciatic foramina

Viscera

Organ/Part of Organ Location/Description Notes
anal canal terminal end of the digestive tract anal canal is continuous with the rectum above and opens at the anus below; it is regulated by external and internal anal sphincters
rectum distal end of the colon rectum begins at about the S3 vertebral level; it is continuous distally with the anal canal

Muscles of the Anal Triangle

Muscle Origin Insertion Action Innervation Artery Notes
anal sphincter, external perineal body or central tendinous point of the perineum encircles the anal canal; superficial fibers attach to the coccyx constricts the anal canal inferior rectal nerves (from the pudendal nerve) inferior rectal a. skeletal (voluntary) muscle, as contrasted with sphincter ani internus, which is smooth (involuntary) muscle; the external anal sphincter is considered part of the pelvic diaphragm
anal sphincter, internal encircles the anal canal encircles the anal canal constricts the anal canal parasympathetic fibers from S4 middle rectal a. smooth muscle (involuntary), as contrasted with sphincter ani externus, which is skeletal muscle (voluntary)

Nerves of the Perineum

Nerve Source Branches Motor Sensory Notes
labial, anterior ilioinguinal n. no named branches none skin of the anterior aspect of the labium majus communicates with the genital br. of the genitofemoral n.
labial, posterior perineal n. (a branch of the pudendal n.) no named branches none skin of the posterior aspect of the labium majus communicates with the perineal br. of the posterior femoral cutaneous n.
pudendal n. ventral primary rami of spinal nerves S2-S4 (sacral plexus) inferior rectal n., perineal n., dorsal n. of the clitoris/penis its branches supply: external anal sphincter, bulbospongiosus m., ischiocavernosus m., superficial & deep transverse perineus mm., sphincter urethrae m., sphincter urethrovaginalis, compressor urethrae its branches supply: skin of the anus, posterior scrotum/labium majus, clitoris/penis pudendal n. passes through the pudendal canal formed by fascia on the medial surface of the obturator internus m.
rectal, inferior pudendal n. no named branches external anal sphincter skin of the anus inferior rectal nerve is one of the first branches of the pudendal n.
scrotal, anterior anterior cutaneous br. of the ilioinguinal n. no named branches none skin of the anterior aspect of the scrotum anterior scrotal n. is the continuation of the ilioinguinal n. at the superficial inguinal ring; it communicates with the genital br. of the genitofemoral n.
scrotal, posterior perineal n., from the pudendal n. no named branches none skin of the posterior aspect of the scrotum posterior scrotal n. communicates with the perineal br. of the posterior femoral cutaneous n.

Arteries of the Perineum

Artery Source Branches Supply to Notes
labial, posterior perineal a. no named branches posterior aspect of the labium majus posterior labial a. courses through the superficial perineal space
perineal internal pudendal a. posterior labial/scrotal; deep br. posterior aspect of the scrotum/labium majus; muscles of the superficial perineal space perineal a. courses superficial to the superficial transverse perineus m.; it courses with the perineal n.
pudendal, deep external femoral a. unnamed muscular branches origins of pectineus m., adductor longus m.; scrotum/labium majus deep external pudendal a. may arise from the medial circumflex femoral a.
pudendal, internal internal iliac a., anterior division inferior rectal a., perineal a., artery of the bulb of the clitoris/penis, urethral a., deep clitoral/penile a., dorsal clitoral/penile a. anus, muscles of the superficial and deep perineal spaces, clitoris/penis, posterior aspect of the scrotum/labium majus internal pudendal a. is the primary blood supply to the perineum
pudendal, superficial external femoral a. no named branches skin and superficial fascia of the upper medial thigh, skin of the pubic region superficial external pudendal a. is one of three superficial branches of the femoral a. near the inguinal ligament (see also: superficial circumflex iliac a., superficial epigastric a.)
rectal, inferior internal pudendal a. no named branches anus, ischioanal fossa inferior rectal a. anastomoses with the middle rectal a. and the superior rectal a.

Veins of the Perineum

Vein Tributaries Drains Into Regions Drained Notes
pudendal, deep external part of the drainage of the superficial dorsal v. of the penis/clitoris femoral skin and superficial fascia of the penis/clitoris; pubic region deep external pudendal v. shares its region of drainage with the superficial external pudendal v.
pudendal, internal deep dorsal v. of the penis/clitoris, v. of the bulb, posterior labial/scrotal v., inferior rectal v. internal iliac crus and bulb of the clitoris/penis; urogenital region, anal region internal pudendal v. passes through the pudendal canal
pudendal, superficial external part of the drainage of the superficial dorsal v. of the penis/clitoris great saphenous skin and superficial fascia of the penis/clitoris; pubic region superficial external pudendal v. shares its region of drainage with the deep external pudendal v.

Topographic Anatomy of the Perineum

Structure/Space Description/Boundaries Significance
anal triangle posterior subdivision of the diamond-shaped perineum; its boundaries are: anteriorly - posterior margin of the perineal membrane (corresponds to an imaginary line connecting the ischial tuberosities); posterolaterally - sacrotuberous ligament anal triangle is the location of the terminal end of the gastrointestinal tract (anus)
ischioanal fossa a fat-filled space located lateral to the anal canal and inferior to the pelvic diaphragm; its boundaries are: superomedially - pelvic diaphragm (anterior recess extends superior to the urogenital diaphragm); medially - external anal sphincter muscle and anal canal; laterally - obturator internus fascia and ischial tuberosity; posterolaterally - sacrotuberous ligament and gluteus maximus m.; (posterior recess extends superior to the gluteus maximus m.) the fat and loose connective tissue in the ischioanal fossa compresses to allow passage of feces; also known as: ischiorectal fossa
natal cleft midline cleft between the buttocks natal cleft lies between the gluteus maximus muscles
perineum a diamond-shaped space forming the outlet of the pelvis; its boundaries are: anterolaterally - inferior pubic ramus, ischial ramus and ischial tuberosity; posterolaterally - sacrotuberous ligament perineum is subdivided into the anal triangle and urogenital triangle by an imaginary line connecting the ischial tuberosities
urogenital triangle anterior subdivision of the diamond-shaped perineum; its boundaries are: anterolaterally - inferior pubic ramus, ischial ramus; posteriorly - posterior margin of perineal membrane (corresponds to an imaginary line connecting the ischial tuberosities) urogenital triangle is the location of the terminal portion of the urinary tract and genital tract

Lymphatics of the Perineum

Structure Location Afferents from Efferents to Regions drained Notes
inguinal nodes, deep along the medial side of the femoral v. deep to the fascia lata and inguinal ligament superficial inguinal nodes, popliteal nodes external iliac nodes lower limb, external genitalia, lower part of the anterior abdominal wall the deep inguinal node in the femoral canal is called the node (or gland) of Cloquet
inguinal nodes, superficial in the superficial fascia parallel to the inguinal ligament and along the terminal part of the greater saphenous v. lymphatic vessels from the superficial lower limb, superficial abdominal wall, perineum external iliac nodes; deep inguinal nodes lower abdominal wall; external genitalia; superficial parts of the lower limb superficial inguinal nodes are 12-20 in number; they become inflamed during infections of the lower limb; they may become inflamed during infections of the external genitalia

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Some of the material presented in these tables is contained in the book:
MedCharts Anatomy by Thomas R. Gest and Jaye Schlesinger
Published by ILOC, Inc., New York. Copyright 1995.

Content of these tables has been edited for use in this course by Patrick W. Tank, Ph.D.
Copyright 2005, Department of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences.

Unauthorized use is prohibited.