Finger comes unaltered from Old English (i.e. Anglo-Saxon). Indeed, the word is found, spelling unchanged, in most of the Germanic languages (e.g. German, Swedish, and Danish); The Dutch get by with vinger.

Each of the fingers have had their own Latin names. Some examples are given in the Aberdeen Beastiary, published in Scotland in the 14th century. (A bestiary is a collection of descriptions of all sorts of animals - some real, some imaginary - and other features of the natural or unnatural world.) From the Bestiary:

• "The [first] finger, index, is also known as salutaris or demonstratorius, the greeting or indicating finger, because we generally use it in greeting, showing or pointing."
• "The [second, middle] finger is called impudicus, lewd; it is frequently used to express the pursuit of something shameful."
• "The [third] is the ring finger, anularis, because it is the one on which a ring is worn. It is also called medicinalis, the medical finger, because it used by physicians to smear on ground-up salves."
• "The [fourth] finger is called auricularis, because we scrape our ear, auris, with it."
  

A digital display: Galileo Galilee's impudicus finger is on exhibit at the Museo di Storia della Scienza in Florence, Italy. www2.jpl.nasa.gov/galileo/finger.html

The sella turcica, a deep depression in the floor of the skull where the pituitary rests, is always translated from the Latin as "Turkish saddle", sella meaning saddle and turcica, "of the Turks". However, for the Romans during most of their empire, sella was a word for stool, not saddle. Indeed, neither the ancient Romans nor Greeks had a word for saddle because they didn't need one: they rode on blankets draped over the horses' backs instead.

While Greeks and Romans were busy perfecting their primitive riding techniques, the Turks and numerous Arab tribes developed and fine-tuned the saddle which, to facilitate rides of great distances, typically had high backrests (or cantles as they came to be called) and relatively tall anterior pommels. Following the introduction of the "European" saddle in the 4th century (called the sella equestris by the Romans) with its lower cantles and usually shorter pommels, the phrase "Turkish saddle" appeared, used by Europeans as a generic reference to any saddle with a high back and front.

Turkish horse saddle circa the 12th century; from God's Warriors: Knights Templar, Saracens and the Battle for Jerusalem, by Dr. Helen J Nicholson and Dr David Nicolle, Osprey Publishing, 2005

An 18th century Arab horse saddle, in the sella turcica style; from Spanish Arms and Armour, By Albert Frederick Calvert, J. Lane Publisher 1907

And so the rationale of using sella turcia in anatomy, which began appearing in medical texts in the 17th century: the saddle-like fossa of the sphenoid bone with a tall posterior "cantle" and anterior "pommel". It's not known who coined the phrase.

A sagittal section through the sphenoid sinus and sella turcica; image modified from Gray's Anatomy (1909) and Wikipedia.com

Sphincter was first used by Galen in the 2nd century, probably as an allusion to the talented constrictor that was the Sphinx of Greek mythology. A chimera with the head of a woman and the body of a winged-lion, and who received her name from the Greek word sphingo, "I strangle", the Sphinx sat outside Thebes and demanded that all passersby answer her riddle: "Which creature travels in the morning on four feet, at noon on two, and in the evening upon three?" She strangled anyone unable to answer. Oedipus finally provided the correct respo...

A fourth century BC kylix from the Vatican Museum showing Oedipus with the Sphinx. en.wikipedia.org/wiki/Image:Oedipus_and_sphinx.jpg

Note that the Grecian Sphinx is not the same as the sphinxes of Egypt: The Greek name "sphinx" was inexplicably applied some 2600 years ago to an Egyptian chimeric lion, even though it is wingless and has the head of a man not a woman. The original Egyptian name of this creature is unknown. The most famous of the Egyptian sphinxes is the Great Sphinx of Giza.

Achilles tendon: the common tendon of the gastrocnemius, soleus, and sometimes the plantaris muscles; also known as the calcaneal tendon. It attaches to the posterior portion of the calcaneus or heel bone.

The name comes indirectly from Greek mythology: After receiving a prophecy that her young son, Achilles, would die in battle, the goddess Thetis dipped him into the magical, protective waters of the river Styx. However, she held him by his heel which was not immersed and thus remained vulnerable. Years later, as luck would have it, Achilles was fatally wounded during the Trojan War: a poison arrow in the back of the foot, a region henceforth known as Achilles heel (and so, metaphorically, an "Achilles heel" is a seemingly insignificant but in fact critical weakness).

It wasn't until 1693 that the term Achilles tendon appeared (chorda Achillis in the original Latin), so named by the resourceful Dutch anatomist Philip Verheyen while dissecting his own amputated leg.

Thetis dipping Achilles in the river Styx. Sculpture by Thomas Banks (1735-1805) Victoria and Albert Museum, London

Philip Verheyen dissecting his Achilles tendon. Artist: anonymous; from the collection of Pieter Deheijde, Amsterdam

Alveolus (pl. alveoli) is derived from the Latin alvus, the diminunitive form of alveus (a channel or cavity). Thus the term is used generally to describe small structures that have a hollowed-out form.

The word was first used in anatomy by Vesalius around 1550 to describe tooth sockets in the mandible and maxillae; for over 300 years this was the only anatomical definition. The French anatomist Rossignol, in 1846, was the first to describe the microscopic air sacs in the lung as alveoli, probably because magnified sections of lung tissue reminded him of a honeycomb (in Latin, the cells of honeycombs were called alveoli, a definition that still holds forth in modern-day English).

The latin root alveus has entered English as well, meaning "river channel". It also is used in anatomy to describe a tract that runs much of the length of the hippocampus and forms the floor of the "channel" that is the temporal horn of the lateral ventricle.

The most recent anatomical use of alveoli, stemming from the latter 19th century, is as an alternative (and superfluous) name for the acini of exocrine glands.

Honeycomb-like alveoli in a cat lung as drawn by Rossignol from Principles of Human Physiology (1860) by William Benjamin Carpenter

Mitral is derived from the Latin mitra, girdle or turban, which gave rise to mitre, the ceremonial head-dress first worn by Roman Catholic bishops. Subsequently the hat was adopted by bishops of the Anglican, Episcopal, and some of the Christian orthodox churches.

A 15th century bishops' mitre on the left, a present-day mitre on the right, and in the middle, a 16th century-style mitre from the time of Vesalius. Adapted from the Catholic Encyclopedia www.newadvent.org

The mitral valve of the heart, positioned between the left atrium and left ventricle, was so named by Vesalius in the 16th century because its two parallel cusps (flaps) resemble of the paired, pointed "horns" or cornua of an (upside-down) bishop's mitre. Thomas Henry Huxley, "Darwin's bulldog" and the person who coined "agnostic", would give his students this mnemonic to remind them the valve was on the left: "a bishop is never in the right."

The mitral valve is also known as the bicuspid valve or the left atrioventricular (AV) valve. The Terminologia Anatomica no longer lists bicuspid.

Mental, in anatomy, is an adjective meaning "related to the chin". It comes from the Latin word for chin, mentum.

Its use is seen in the mentalis, a muscle covering the tip of the chin, and the mental foramen, a small passageway found near the chin on each side of the mandible through which the mental artery, vein, and nerve pass.

Across all cultures it is common for people to touch their their chins as they ponder, but mental as in "mental images" comes from mens, Latin for mind, and not from mentum. However, as mentum is so closely linked to mens through our behavior, some etymologists believe (albeit without evidence) that both words are somehow etymologically related.

The Thinker by Auguste Rodin: engaged
in two types of mental activity.

Fornix (plural, fornices), comes directly from the Latin word for a vault, i.e., a small room with an arched ceiling. Often the term was by the Romans in specific reference to rooms occupied by slaves or the poor. Street prostitutes were known to provide their services in fornices; hence the word "fornication".

The use of fornix in anatomy includes:

• The left and right fornices of the brain's limbic system, formed by white matter tracts that arch over the diencephalon,
  
• The vaginal fornix, the vaulted space in the vagina that surrounds the cervix of the uterus
• The gastric fornix, a term used in radiology for the internal arch of the fundus.
  

A series of fornices in Roman ruins, Gaeta, Italy, with the front walls and doors long gone. Modifed from A Dictionary of Roman Antiquities, by Antony Rich, Appelton, 1874.