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Muscles and Fascia of the PerineumVI. MUSCLES OF THE PERINEUM The perineum corresponds to the outlet of the pelvis. Its deep boundaries are--in front, the pubic arch and the inferior pubic ligament; behind; the tip of the coccyx; and on each side the inferior ramus of the pubis and the ramus of the ischium, the ischial tuberosity and the sacrotuberous ligament. The space within these boundaries is somewhat lozenge-shaped. On the surface of the body the perineum is limited by the scrotum in front, the buttocks behind, and the medial sides of the thighs laterally. A line drawn transversely in front of the isebial tuberosities divides the space into two portions. The posterior contains the termination of the anal canal, and is known as the anal region; the anterior contains the external urogenital organs, and is termed the urogenital region. The muscles of the perineum may therefore be divided into two groups
1. THE MUSCLES OF THE ANAL REGION
The superficial fascia is very thick, areolar in texture, and contains much fat in its meshes. On each side a pad of fatty tissue extends deeply between the Levator ani and Obturator internus into a space known as the ischiorectal fossa. The deep fascia forms the lining of the ischiorectal fossa; it comprises the anal fascia, and that part of the obturator fascia which lies below the origin of Levator ani. Ischiorectal fossa.--The fossa is somewhat wedge-shaped, with its base directed to the surface of the perineum, and its thin edge at the line of meeting of the obturator and anal fasciae. It is bounded medially by the Sphincter ani externus and the anal fascia; laterally, by the tuberosity of the ischium and the obturator fascia; anteriorly, by the perineal membrane (inferior fascia of the urogenital diaphragm); posteriorly, by the Gluteus maximus and the sacrotuberous ligament. Crossing the space transversely are the inferior rectal vessels and the inferior hemorrhoidal nerve; at the posterior part are the perineal and perforating cutaneous branches of the sacral plexus; while from the anterior part the scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie on the lateral wall of the fossa in the pudendal canal. The fossa is filled with fatty tissue, across which numerous fibrous bands extend. The Corrugator cutis ani forms a thin stratum of involuntary muscular fibers which radiate from the anal orifice. Medially the fibers fade off into the subcutaneous tissue; laterally they blend with the true skin. When the muscle contracts the skin around the anus is raised into ridges. The Sphincter ani externus (figs. 615, 617) is a flat sheet of muscular fibers, elliptical in shape and intimately adherent to the skin surrounding the anus. It measures from 8 to 10 cm in length and is about 2.5 cm in width opposite the anus. It consists of two portions, superficial and deep. The superficial portion constitutes the chief part of the muscle, and arises by a narrow tendinous band from the tip of the coccyx; the muscle consists of two flattened sheets which pass one on each side of the anus and meet in front to be inserted into the perineal body (central tendinous point of the perineum), joining with the Transversus perinei superficialis, the Levator ani, and the Bulbospongiosus (Bulbocavernosus). The deep portion, forms a complete sphincter to the axial canal. Its fibers surround the canal, closely applied to the Puborectalis and the Sphincter ani internus, and in front blend with the other muscles at the perineal body. In a considerable proportion of cases the fibers decussate in front of the anus, and are continuous with the Transversi perinei superficiales. Posteriorly they are not attached to the coccyx, but are continuous with those of the opposite side behind the anal canal. The upper edge of the muscle is ill-defined, since it receives numerous fibers from the Puborectalis.
 Nerve-supply.-The Sphincter ani externus is supplied by a branch from the fourth sacral nerve and by twigs from the inferior hemorrhoidal branch of the pudendal nerve, Actions.-The Sphincter ani externus is normally in a state of tonic contraction, aid having no antagonistic muscle it keeps the anal canal and orifice closed. It can be put into a condition of greater contraction under the influence of the will, so as to occlude the anal aperture more firmly. Taking its fixed point at the coccyx, it helps to fix the perineal body (central point of the perineum). The Sphincter ani internus is a muscular ring which surrounds about 2.5 cm. of the anal canal; its inferior border is in contact with, but distinct from, the deep surface of the Sphincter ani externus and, posteriorly and on each side, it is covered by the Puborectalis. It is about 5 mm. thick, and is formed by an aggregation of the involuntary circular fibers of the intestine. Its lower border is about 6 mm. from the orifice of the anus. Actions --- Its action is entirely involuntary. It helps the Sphincter ani externus and the Puborectalis to occlude the anal canal. |
 Gray's Anatomy 1. Embriology 2. Osteology  Vertebral Column
General Characteristics of a VertebraCervical VertebraThoracic VertebraLumbar VertebraSacral and Coccygeal VertebraVertebral Column as a WholeSternumRibsCostal CartilagesThorax Skull
Introduction Exterior SkullSuperior viewAnterior viewOrbitLateral viewPosterior viewInferior view Interior SkullIntroduction & Skull CapAnterior Cranial FossaMiddle Cranial FossaPosterior Cranial FossaNasal cavityMandibleHyoid Bone Cranial Bones
Occipital BoneSphenoid BoneTemporal BonesParietal BonesFrontal BoneEthmoid BoneInferior Nasal ConchaLacrimal BonesNasal BonesVomerSutural Bones Facial Bones
MaxillaPalatine BoneZygomatic BoneDifferences in Skull due to AgeSex Differences in Skull & Craniology Extremities
Extremities Upper Extremity BonesScapulaClavicleHumerusRadiusUlna HandSkeleton of the HandCarpalsMetacarpalsPhalanges of the HandOssification of bones of the Hand Lower Extremity BonesHip BonePelvisFemurPatellaTibiaFibula FootSkeleton of the FootTarsalsMetatarsalsPhalanges of the FootOssification of bones of the FootComparison of the Bones of the Hand and FootSesamoid Bones 3. Arthrology Trunk Articulations
Mandibular joint (temporomandibular joint) Vertebral Column ArticulationsJoints of the Vertebral BodiesJoints of the Vertebral ArchesSacrococcygeal JointAtlantoaxial Articulation (C1-C2)Vertebral Column with the CraniumCostovertebral ArticulationsSternocostal ArticulationsInterchondral ArticulationsSternal ArticulationsMechanism of the Thorax Upper Extremity Articulations
Sternoclavicular (SC) JointAcromioclavicular (AC) JointLigaments of the ScapulaShoulder Joint (glenohumeral – GH)Elbow JointRadioulnar JointsRadiocarpal Joints (wrist-joint)Intercarpal ArticulationsCarpometacarpal & Intermetacarpal ArticulationsMetacarpophalangeal ArticulationsInterphalangeal Joints Pelvis Articulations
Lower Extremity Articulations
Hip-joint (acetabulofemoral joint - AF)Knee jointTibiofibular JointsAnkle-joint (talocrural)Intertarsal ArticulationsTarsometatarsal & Intermetatarsal ArticulationsMetatarsophalangeal & Interphalangeal ArticulationsArches of the Foot 4. Myology Muscles of the Head
Muscles of the ScalpMuscles of the EyelidMuscles of the NoseMuscles of the MouthMuscles of Mastication Muscles of the Anterolateral Region of the NeckAnterolateral RegionSuperficial & Lateral Cervical MusclesSupra and Infrahyoid MusclesAnterior Vertebral MusclesLateral Vertebral Muscles Muscles of the Trunk
Deep Muscles of the BackSuboccipital MusclesMuscles of the ThoraxMechanism of RespirationMuscles and Fascia of the AbdomenMuscles and Fascia of the PelvisMuscles and Fascia of the PerineumMuscles of the Urogenital Region - MaleMuscles of the Urogenital Region - Female Muscles of the Upper Extremity
Muscles Connecting the Upper Extremity to the Vertebral ColumnMuscles Connecting the Upper Extremity to the Thoracic WallsMuscles and Fascia of the ShoulderMuscles and Fascia of the ArmMuscles and Fascia of the ForearmMuscles and Fascia of the Hand Muscles of the Lower Extremity
Muscles and Fascia of the Iliac Region Muscles and Fascia of the ThighAnterior Femoral MusclesMedial Femoral MusclesMuscles of the Gluteal RegionPosterior Femoral Muscles Muscles and Fascia of the LegAnterior Shin (crural) MusclesPosterior Crural MusclesLateral Crural MusclesFascia Around the AnkleMuscles and Fascia of the Foot 5. Angiology Thoracic Cavity
6. The Arteries Arteries of the Head and Neck
a) Common Carotid ArteryRelationsExternal Carotid Artery Triangles of the Neck Internal Carotid Arteryb) Arteries of the Brain Arteries of the Upper Extremity
Arteries of the Trunk
Descending Aorta Thoracic Aorta Abdominal Aorta Common Iliac Arteries Hypogastric Artery External Iliac Artery Arteries of the Lower Extremity
Femoral Artery Popliteal Fossa Popliteal Artery Anterior Tibial Artery Dorsalis Pedis ArteryPosterior Tibial Artery 7. The Veins Systemic Veins
Veins of the Heart Veins of the Head and NeckVeins of the Exterior of the Head and FaceVeins of the Neck Diploic Veins Veins of the Brain Venous Sinuses of the Dura Mater (Opthalmic and Emissary Veins)Veins of the Upper Extremity and Thorax Veins of the Lower Extremity, Abdomen, and Pelvis 8. The Lymphatic System 9. Neurology Brain or Encephalon
IntroductionHind-brain or RhombencephalonMid-brain or MesencephalonFore-brain or ProsencephalonComposition and Central Connections of the Spinal NervesComposition and Central Connections of the Spinal Nerves 2Pathways from the Brain to the Spinal CordMeninges of the Brain and Medulla Oblongata (Spinalis)Cerebrospinal Fluid Cranial Nerves
Introduction1. Olfactory Nerves2. Optic Nerve3. Oculomotor Nerve4. Trochlear Nerve5. Trigeminal Nerve6. Abducent Nerve7. Facial Nerve8. Acoustic Nerve9. Glossopharyngeal Nerve10. Vagus Nerve11. Accessory Nerve12. Hypoglossal Nerve Spinal Nerves
IntroductionPosterior DivisionsAnterior DivisionsThoracic NervesLumbosacral PlexusSacral and Coccygeal Nerves Sympathetic Nerves
IntroductionCephalic Portion of the Sympathetic SystemCervical Portion of the Sympathetic SystemThoracic Portion of the Sympathetic SystemAbdominal Portion of the Sympathetic SystemPelvic Portion of the Sympathetic SystemGreat Plexuses of the Sympathetic System 10. The Organs of the Senses and the Common Integument The Peripheral Organs of the Special Senses
a. The Organs of Tasteb. The Organ of Smellc. The Organ of Sight 1. The Tunics of the Eye 2. The Refracting Media 3. The Accessory Organs of the Eyed. The Organ of Hearing 1. The External Ear 2. The Middle Ear or Tympanic Cavity 3. The Auditory Ossicles 4. The Internal Ear or Labyrinthe. Peripheral Terminations of Nerves of General Sensations 11. Splanchnology The Respiratory Apparatus
The Respiratory Apparatus a. The Larynx b. The Trachea and Bronchi c. The Pleurae d. The Mediastinum e. The Lungs The Digestive Apparatus
The Digestive Apparatus a. The Mouth b. The Fauces c. The Pharynx d. The Esophagus e. The Abdomen f. The Stomach g. The Small Intestine h. The Large Intestine i. The Liver j. The Pancreas The Urogenital Apparatus
a. Development of the Urinary and Generative OrgansDevelopment of the Urinary and Generative Organs b. The Urinary Organs 1. The Kidneys 2. The Ureters 3. The Urinary Bladder 4. The Male Urethra 5. The Female Urethra c. The Male Genital Organs 1. The Testes and their Coverings 2. The Ductus Deferens 3. The Vesiculae Seminales 4. The Ejaculatory Ducts 5. The Penis 6. The Prostate 7. The Bulbourethral Glands d. The Female Genital OrgansThe Female Genital Organs 1. The Ovaries 2. The Uterine Tube 3. The Uterus 4. The Vagina 5. The External Organs 6. The Mammae The Ductless Glands
a. The Thyroid Glandb. The Parathyroid Glandsc. The Thymusd. The Hypophysis Cerebrie. The Pineal Bodyf. The Chromaphil and Cortical Systemsg. The Spleen 12. Surface Anatomy and Surface Markings Muscle Tables
Muscles of facial expressionMuscles of masticationEye movementPalatePharynxLarynxTongue musclesHyoid MusclesAnterior & Lateral NeckPrevertebralPosterior Neck MusclesSuperficial backDeep backShoulder musclesArm musclesAnterior ForearmPosterior ForearmHand musclesThoracic wallAnterior abdominal wallPosterior abdominal wallPelvic floor musclesGluteal regionPosterior thighAnterior thighMedial thighAnterior & lateral legPosterior legFoot Quizzes 1. Introduction
Anatomical TermsBody RegionsSkeleton IntroductionBones Hand-FootLandmarksJoint ClassificationsActionsMuscle ShapesMuscles Introduction 2. Head & Face
3. Neck
4. Torso
Trunk BonesAnterior TrunkTorso JointsAbdominal Muscles IntroductionBack Muscles IntroductionBack Muscles SuperficialBack Muscles DeepBack Muscles TransversospinalisVertebrae Detailed 5. Shoulder & Arm
6. Forearm, Wrist & Hand
BonesLigamentsAnterior Muscles IntroductionPosterior Muscles IntroductionThenar MusclesCentral Hand MusclesHypothenar Muscles 7. Hip, Thigh & Knee
8. Leg, Ankle & Foot
BonesLigamentsAnterior Leg MusclesLateral Leg MusclesPosterior leg SuperficialPosterior Leg DeepFoot Muscles
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