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A personal message from Dr Mark Hill (May 2020)  
Mark Hill.jpg
I have decided to take early retirement in September 2020. During the many years online I have received wonderful feedback from many readers, researchers and students interested in human embryology. I especially thank my research collaborators and contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link


Finger length ratio
Finger length ratio - 2D4D


The ratio of 2nd and 4th finger (digit) length. This ratio has been suggested to relate to high fetal testosterone concentration (males have lower 2D:4D than females) and also thought to be an indicator of various neurological abnormalities. To measure, using your right hand palm up, measure the index finger (2) and ring finger (4) length from palm to tip. Dividing the index finger by the ring finger gives the 2D:4D ratio, average women ratio is 1, average men is 0.98 (human PMID 16504142, alternative result for mice PMID 19495421).
(More? Image - 2D:4D ratio | Limb Development | Neural System - Abnormalities | Endocrine System Development | PMID 16504142)

3D echocardiography

An ultrasound cardiac diagnostic technique.
(More? Ultrasound | Cardiovascular System Development | Cardiac Abnormalities)

3rd ventricle

(third ventricle) A fluid-filled space formed from neural tube lumen, located within the diencephalon (from the primary vesicle, prosencephalon or forebrain). In the adult this region lies between the two thalamic bodies. The massa intermedia passes through it and the hypothalamus forms its floor and part of its lateral walls.
(More? Lecture - Ectoderm Development | Ventricular System | Neural System Development)

4th ventricle

(fourth ventricle) A fluid-filled space formed from neural tube lumen, located within the rhombencephalon (from the primary vesicle, hindbrain). This ventricle is connected to the subarachnoid space via two lateral foramina of Luschka and by one medial foramen of Magendie.
(More? Lecture - Ectoderm Development | Ventricular System | Neural System Development)
Cranial Nerve Development
Cranial Nerve s


Human cranial nerve (CN) are traditionally represented by Roman numerals. These are paired nerves emerging from the brain and not the spinal cord.
I - Olfactory nerve (sensory) II - Optic Nerve (sensory) III - Oculomotor nerve (mainly motor) IV - Trochlear nerve (mainly motor) V - Trigeminal nerve (both sensory and motor) VI - Abducens nerve (mainly motor) VII - Facial nerve (both sensory and motor) VIII - Vestibulocochlear nerve (auditory-vestibular nerve or statoacoustic nerve; mostly sensory) IX - Glossopharyngeal nerve (both sensory and motor) X - Vagus nerve (both sensory and motor) XI - Accessory nerve (cranial accessory nerve or spinal accessory nerve; mainly motor) XII - Hypoglossal nerve (mainly motor)
(More? Cranial Nerve Development | Neural System Development)

Glossary Comments

Use this page to access brief definitions of specific embryology terms. Additional information can be accessed from links listed at the end of each definition. Glossary from the UNSW Embryology program compiled and written by Dr Mark Hill. Reference material used in preparing this glossary list includes: texts listed on page 1 "Reading" of each notes section, Department of Anatomy Publications, WWW resources from NCBI, NIH, OMIM, NHMRC (Australia), AMA (USA), Office of Rare Diseases (USA), PubMed Medline Dictionaries, MSDS, Merck Manual home edn. and WHO ART terminology (2009).

These notes are for Educational Purposes Only Please email Dr Mark Hill if you wish to make a comment about this current project.

Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link

Cite this page: Hill, M.A. (2020, June 6) Embryology Numbers. Retrieved from

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© Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G