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List of Threes in Anatomy

The structure of the human body is organized into groups of three with remarkable frequency. I have listed several examples of this tendency by region. This list does not include structures contributing to form the many “triangles” in the body. If you know of any more, please let me know.

John A. McNulty, Ph.D.

Historically, this was the first hyperlink to the Book of Threes in 1996 thanks to John McNulty . . .

Michael Eck – Author The Book of Threes

To visit John McNulty’s amazing list, click here.

Snapshot ofJohn McNulty’s amazing list 10.2018

The structure of the human body is organized into groups of three with remarkable frequency. I have listed several examples of this tendency by region. This list does not include structures contributing to form the many “triangles” in the body. If you know of any more, please let me know John A. McNulty, Ph.D.


General




    3 body planes - frontal
              sagittal
              transverse
              
    3 layers of skin- epidermis
              dermis
              hypodermis

    3 general venous circulations- systemic
              pulmonary
              portal          

Embryology



    3 germ layers-  endoderm
            mesoderm
            ectoderm

    3 divisions of somites- sclerotome
                dermatome
                myotome

    3 definitive kidneys-   pronephros
                mesonephros
                metanephros
                
    3 derivatives of skull- desmo/dermatocranium
                splanchno/viscerocranium
                chondrocranium
                
    3 initial embryonic divisions of the brain- prosencephalon
                            mesencephalon
                            rhombencephalon

Back



    3 parts of the erector spinae m.-   iliocostalis
                        longissimus
                        spinalis
            each are divided again into 3 parts

    3 parts of the transversospinalis m. -  semispinalis m.
                        multifidus m.
                        rotator m.

    3 coverings of the spinal cord- dura mater
                        arachnoid
                    pia
                    
    3 spaces surrounding spinal cord-   epidural
                            subdural
                        subarachnoid

    3 borders of the scapula-   medial (vertebral)
                    lateral
                    superior

    3 angles of the scapula


Neck



    3 parts of the axillary artery
        3rd part has 3 branches-    subscapular
                        anterior humeral circumflex
                        posterior humeral circumflex
                    
    Brachial plexus
        3 trunks-   upper
                middle
                lower
        3 posterior divisions
        3 anterior divisions
        3 cords-    lateral
                medial
                    3 branches off medial cord- medial brachial
                                    medial antebrachial
                                    medial pectoral
                posterior
                    3 branches off posterior cord- upper subscapular
                                    lower subscapular
                                    thoracodorsal

    3 branches off the thyrocervical trunk- transverse cervical
                        suprascapular
                        inferior thyroid
                        
    3 veins drain the thyroid gland -   superior (into internal jugular)
                        middle (into internal jugular)
                        inferior (into left brachiocephalic)
                        
    3 scalene muscles-      anterior
                    middle
                    posterior

    3 muscles attach to spine of C2-    semispinalis cervicis
                        obliquus capitis inferior
                        rectus capitis posterior major
                    
    3 constrictor muscles-  superior
                middle
                inferior
                    
    3 parts of the pharynx- nasopharynx
                oropharynx
                laryngeopharynx
                    
    3 parts to the hyoid bone-  body
                    greater horn
                    lesser horn
                    
    3 structures inside carotid sheath- common carotid artery
                        internal jugular vein
                        vagus nerve
                        
    3 ganglia in sympathetic cervical chain-    superior (magnum)
                            middle
                            inferior (stellate)


Head



    3 parts of the maxillary artery-    mandibular
                        pterygoid
                        pterygopalatine
                        
    3 divisions of the trigeminal n.-   V1 - ophthalmic - has 3 branches
                            frontal
                            nasociliary
                            lacrimal
                        V2 - maxillary
                        V3 - mandibular- has 3 parts
                            undivided trunk
                            anterior division
                            posterior division-  has 3 branches
                                auriculotemporal
                                lingual
                                inferior alveolar
                                
    3 cranial fossae-   anterior
                middle
                posterior
                    
    3 nuchal lines- inferior
            superior
            highest

    3 layers to calvarium-      outer table
                    diploe
                    inner table
    
    3 clinoid processes of the sphenoid bone- anterior
              middle
              posterior

    3 cranial nerves pass through jugular foramen-  C.N. IX
                            C.N. X
                            C.N. XI
                                                    
    3 cranial nerves travel in the wall of the cavernous sinus- C.N. III
                                    C.N. IV
                                    C.N. V
                                    
    3 cranial nerves carry parasympathetics to the head-    C.N. III
                                C.N. VII
                                C.N. IX
                                
    3 nasal conchae-    superior
                middle
                inferior

    3 principal components of the temporal bone-    squama
                            petro/mastoid
                            tympanic ring

    3 bones of the upper jaw/palate-    premaxilla
                        maxilla
                        palatine
                
    3 salivary glands-  parotid
                submaxillary
                sublingual
                
    3 muscles innervated by 3 cranial nerves attach to the styloid process-         
                stylohyoid - C.N. VII
        stylopharyngeus - C.N. IX
        styloglossus - C.N. XII
        
    3 layers in tympanic membrane (derived from 3 germ layers)
                                    
    3 cranial nerves innervate the external tympanum-   C.N. V
                                C.N. VII
                                C.N. X

    3 middle ear bones- incus
                malleus
                stapes
                
    3 parts of the ear- outer
                middle
                inner
                
    3 semicircular canals
    
    3 membranes of the cochlea- Reissner
                Tectorial
                Basilar
                
    3 intrinsic muscles of the tongue-  longitudinal
                        vertical
                        transverse
                                                                            
    3 muscles elevate the mandible- masseter m.
                            temporalis m.
                            medial pterygoid m.
                        
    3 branches of the posterior auricular artery-   stylomastoid branch
                        auricular branch
                        occipital branch
                        
    3 branches of the ophthalmic nerve (VI)-    nasociliary n.
                        frontal n.
                        lacrimal n.
                                                                            
    3 superior alveolar nerves- anterior superior alveolar n.
                            middle superior alveolar n.
                            posterior superior alveolar n.
                        
    3 types of deciduous teeth- incisors
                    canine
                    molars

    3 layers of dentition-  enamal
                dentin
                pulp
                    
    3 general layers of the eye -   retinal
                    choroidal/ciliary body
                    scleral/corneal
                    
    3 color receptors in cone cells -   red
                        blue
                        yellow
                        
    3 nerves to the larynx -  external laryngeal n.
                        internal laryngeal n.
                        recurrent laryngeal n.
                                        
    3 cerebral arteries -       anterior
                    middle
                    posterior

    3 arteries supply the cerebellum -  superior cerebellar
                        anterior inferior cerebellar
                        posterior inferior cerebellar


Shoulder



    3 muscles attach to coracoid process -  coracobrachialis
                        pectoralis minor
                        short head of biceps
                        
    3 parts of the axillary a.; 3rd part has 3 branches-    subscapular a.
                                anterior circumflex humeral a.
                                posterior circumflex humeral a
                                
    3 muscles of the rotator cuff are rotators
    
    3 glenohumeral ligaments - superior
                        middle
                        inferior

Arm



    3 muscles in anterior comparment-   biceps brachii
                        coracobrachialis
                        brachialis
                            
    3 heads of triceps brachii m.-  long
                    lateral
                    medial
                            
    3 muscles attach to greater tubercle of the humerus-    supraspinatus
                                infraspinatus
                                teres minor

    3 parts of the ulnar collateral ligament of the elbow - anterior
                            posterior
                            oblique



Forearm



    3 muscles in deep anterior compartment -    flexor digitorum profundus
                            flexor pollicis longs
                            pronator quadratus


Hand



    3 muscles in thenar eminence-   opponens pollicis
                    flexor pollicis brevis
                    abductor pollicis brevis
                    
    3 muscles in hypothenar compartment-    flexor digiti minimi
                        abductor digiti minimi
                        opponens digiti minimi
                            
    3 phalanges in fingers- proximal
                middle
                distal
                    
    3 palmer interossei


Thorax



    3 compartments- mediastinum
            left pleural cavity
            right pleural cavity
            
    3 branches off the aortic arch- brachiocephalic a.
                    left common carotid a.
                    left subclavian a.
                    
    3 parts of the aorta-   ascending
                arch
                descending
                
    3 principal surfaces of the pleura- costal
                        diaphragmatic
                        mediastinal
                            *the cupola is the superior extension
                            
    3 lobes of the right lung-  superior
                    middle
                    inferior
                    
    3 bronchopulmonary segments of the upper right lobe-    apical                                  
                                posterior
                                anterior

    3 muscles of interthoracic wall-    external intercostal                                    
                        internal intercostal
                        intercostalis intimus
                                
    3 false ribs on each side
    
    3 cusps of the semilunar aortic and pulmonary valves of the heart
    
    3 cusps of the tricuspid valve
    
    3 main arteries of the heart-   circumflex
                    anterior interventricular
                    right coronary
                    
    3 splanchnic nerves-    greater
                lesser
                least



Abdomen



    3 folds in anterior abdominal wall- median (obliterated urachus)
                        medial (obliterated umbilical a.)
                        lateral (inferior epigastric a.)

    3 muscles contribute to linea semilunaris/rectus abdominus aponeurosis -
                internal oblique
                external oblique
                transversus abdominus
                        
    3 openings in diaphragm-    aortic
                    esophageal
                    inferior vena cava
                    
    3 arcuate ligaments of diaphragm-   median over aorta
                        medial over psoas major m.
                        lateral over quadratus lumborum m.
                        
    3 parts of the stomach- fundus
                body
                pylorus
                
    3 smooth muscle layers of the stomach-  oblique
                        longitudinal
                        circular

    3 unpaired branches of the abdominal aorta- celiac a.
                            superior mesenteric a.
                            inferior mesenteric a.
                            
    3 branches of celiac a.-        left gastric a.
                    splenic a.
                    common hepatic a.
                    
    3 branches of common hepatic a.-    right gastric a.
                        proper hepatic a.
                        gastroduodenal a.

    3 arterial branches supply adrenal glands-  inferior phrenic
                            aorta
                            renal
                            
    3 structures lie within porta hepatis-      proper hepatic a.
                            portal vein
                            common bile duct
                            
    3 principal veins contribute to the portal vein-    splenic v.
                                superior mesenteric v.
                                inferior mesenteric v.
                                
    3 parts of the small intestine- duodenum
                    jejunum
                    ileum
                    
    3 parts of large intestine- ascending
                    transverse
                    descending
                    
    3 tenia of large intestine
    
    3 coverings of the spermatic cord-  external spermatic fascia
                        cremasteric fascia
                        internal spermatic fascia
    
    3 vessels in the umbilical cord
                        umbilical vein
                        2 umbilical arteries
    



Pelvis and Perineum



    3 bones in os coxae-    pubis
                ilium
                ischium
                
    3 parts of the pubis-   body
                superior ramus
                inferior ramus
                
    3 foramina in the pelvis-   obturator foramen
                    greater ischiadic foramen
                    lesser ischiadic foramen
                    
    3 gluteus muscles-  gluteus maximus
                gluteus medius
                gluteus minimus
                
    3 rectal arteries-  superior rectal from inferior mesenteric a.
                middle rectal from internal iliac a.
                inferior rectal from internal pudendal a.
                
    3 branches of the posterior division of internal iliac a.-  iliolumbar
                                    lateral sacral
                                    superior gluteal
                                    
    3 openings in the urinary bladder-  left ureter
                        right ureter
                        urethra
                
    3 parts of the urethra- prostatic
                membranous
                spongy
                
    3 parts of the uterus-  fundus
                body
                cervix
                
    3 erectile compartments of the penis-   corpus spongiosum
                        left corpus cavernosum
                        right corpus cavernosum
                        
    3 muscles in superficial perineal pouch-    bulbospongiosus
                            ischiocavernosus
                            superficial transverse perineus
                            
    3 arteries supply the rectum-   superior rectal (from inferior mesenteric)
                    middle rectal (from internal iliac)
                    inferior rectal (from internal pudendal)
                    
    3 valves in the rectum- superior
                middle
                inferior


Gluteus



    3 gluteal muscles-  gluteus maximus
                gluteus medius
                gluteus minimus
                
    3 muscles innervated by superior gluteal n.-    gluteus medius
                            gluteus minimus
                            tensor fascia lata



Thigh



    3 hamstring muscles-    biceps femoris
                semitendinosus
                semimembranosus
                
    3 compartments in the femoral sheath
    
    3 muscular compartments of the thigh-   anterior
                        medial
                        posterior
                        
    3 branches of the lateral femoral circumflex a.-    descending branch
                                transverse branch
                                ascending branch
                                
    3 muscles contribute to the pes anserinus-   sartorius
                            semitendinosus
                            gracilis


Leg



        3 compartments in the leg
        
        3 muscles in anterior compartment - tibialis anterior
                        extensor digitorum
                        extensor hallucis
                        
        3 branches of the peroneal artery in the leg -  anterior tibial a.
                            posterior tibial a.
                            peroneal a.
    
        3 peroneal muscles in the leg - peroneus longus m.
                            peroneus brevis m.
                            peroneus tertius m.
                            
        3 muscles that comprise the triceps surae - grastrocnemius m.
                            soleus m.
                            plantaris m.
                            
        3 muscles in the deep posterior compartment -   tibialis posterioris m.
                            flexor hallucis longus m.
                            flexor digitorum longus m.

Foot



    3 cuneiform bones-  medial
                intermediate
                lateral
                
    3 phalanges in toes-    proximal
                middle
                distal
                
    3 plantar interossei

                
    3 described arches -    medial
                lateral
                transverse

Miscellaneous

    3 exams in the course

If you like this kind of stuff, you may want to visit Michael Eck’s Book of Threes

Other contributors include:

    Lora Leuzinger

  1. Diego Villa Restrepo
  2. Cindy Kuiper
  3. Erika Goodwin
  4. Rob Grieve

 

Please contact: John A. McNulty, Ph.D.