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
- Diego Villa Restrepo
- Cindy Kuiper
- Erika Goodwin
- Rob Grieve
| Please contact: John A. McNulty, Ph.D. |
