Pelvis Anatomy Set 1

The prostatic urethra is the widest and most dilatable part of the male urethra

Weak areas of the pelvis include the pubic
rami, acetabula, sacroiliac joint, and alae of the
ilium

The two main nerves of the sacral plexus
include the sciatic and pudendal. The sciatic
nerve is the largest and broadest nerve in the
body. It is formed by the ventral rami of L4-S3,
which converge on the anterior surface of the
piriformis. The sciatic nerve usually passes
through the greater sciatic foramen, inferior
to the piriformis, to enter the gluteal region

The ureters are muscular tubes, 25 to 30 cm long, that connect the kidneys to the urinary bladder. They are retroperitoneal, with their superior halves in the abdomen and their inferior halves in the pelvis. The pelvic part of the ureters begins where it crosses the bifurcation of the common iliac artery

The pubis is an angulated bone with a
superior ramus that helps to form the acetabulum and an inferior ramus that helps to form
the obturator foramen. A thickening on the anterior part of the body of the pubis is the pubic
crest, which ends laterally as a prominent
bump, the pubic tubercle. The lateral part of the
superior ramus has an oblique ridge known as
the pecten pubis or pectineal line of the pubis

When a person is in the anatomical position, the anterior superior iliac spines and the
anterior aspect of the pubic symphysis lie in the
same vertical plane

Parasympathetic fibers to the bladder are derived from the pelvic splanchnic nerves. They are motor to the detrusor muscle and inhibitory to the internal sphincter. Sympathetic fibers to the bladder are derived from T11 through L2

The ductus deferens begins in the tail of the epididymis and ascends in the spermatic cord. It passes through the inguinal canal and enters the pelvis. It ends by joining the duct of the seminal vesicle to form the ejaculatory duct. It descends medial to the ureter and seminal vesicle

The pelvic inlet is bounded by the superior
margin of the pubic symphysis anteriorly, posterior border of the pubic crest, pecten pubis,
arcuate line of the ilium, anterior border of the
ala of the sacrum, and the sacral promontory

The pelvic girdle is formed by the hip (ischium, pubis, and ilium) bones and the sacrum

The concavity between the ischial spine
and the ischial tuberosity is the lesser sciatic
notch. The larger concavity, the greater sciatic
notch, is superior to the ischial spine and is
formed in part by the ilium

The internal surface of the posterior wall of the prostatic urethra has a median ridge known as the urethral crest. A groove on each side, known as the prostatic sinus, receives the prostatic ductules. A rounded eminence located in the middle of the median ridge is known as the seminal colliculus. The prostatic utricle is an embryonic remnant of the uterus and part of the vagina. The ejaculatory ducts open beside the prostatic utricle

The sacral sympathetic trunks descend posterior to the rectum in the extraperitoneal connective tissue and send gray rami communicantes to each of the ventral rami of the sacral and coccygeal nerves. Each of the sacral trunks is smaller than the lumbar trunks and usually has four sympathetic ganglia

Ducts of the bulbourethral glands empty into the urethra. The seminal vesicles are elongated structures that lie between the fundus of the bladder and the rectum, and they do not store sperm. They secrete a thick, alkaline fluid that mixes with the sperm as they pass into the ejaculatory ducts to the urethra. The superior ends of the seminal vesicles are covered with peritoneum and lie posterior to the ureters, where the rectovesical pouch separates them from the rectum. The inferior ends of the seminal vesicle are separated from the rectum by the rectovesical septum

Four main arteries enter the lesser or true pelvis. The internal iliac and ovarian arteries are paired, and the median sacral and superior rectal arteries are unpaired. The testicular artery does not enter the true pelvis, as it follows the testes through the inguinal canal into the scrotum

The bony framework of the lateral pelvic
walls is formed by the hip bones and the obturator foramen, which is closed by the obturator
membrane. The obturator internus muscles
cover and thus pad most of the lateral pelvic
walls

The piriformis muscles cover the posterolateral wall of the pelvis. The pelvic floor is
formed by the funnel-shaped pelvic diaphragm,
which consists of the levator ani and coccygeus.
The levator ani includes the pubococcygeus,
puborectalis, and iliococcygeus

The superior gluteal nerve arises from the
posterior divisions of the ventral rami of L4 through S1 and leaves the pelvis through the
greater sciatic foramen, superior to the piriformis

The pudendal nerve is derived from the
anterior divisions of the ventral rami of S2
through S4. It accompanies the internal pudendal artery and leaves the pelvis through the
greater sciatic foramen between the piriformis
and coccygeus muscles. It is the main nerve of
the perineum and the chief sensory nerve of the
external genitalia

The uvula of the bladder is a slight projection of the trigone of the bladder. It is usually more prominent in older men

The pelvic splanchnic nerves merge with the hypogastric nerves to form the inferior hypogastric (and pelvic) plexuses

The paraurethral glands are homologues to the prostate. They have common paraurethral ducts, which open, one on each side, near the external urethral orifice

The superior gluteal and iliolumbar arteries arise from the posterior division of the internal iliac arteries. The gonadal arteries arise from the abdominal aorta and the superior rectal arteries from the inferior mesenteric artery. The umbilical, obturator, uterine, vaginal, internal pudendal, and inferior gluteal arteries arise from the anterior division of the internal iliac arteries

The superior boundary of the pelvic cavity
is the pelvic inlet. The pelvis is limited inferiorly by the pelvic outlet, which is closed by the
musculofascial pelvic diaphragm and bounded
posteriorly by the coccyx and anteriorly by the
pubic symphysis

The internal iliac artery is the artery of the pelvis; however, it does supply branches to the buttocks, thighs, and the perineum