Antiseptic (Lat. anti, against, and sepsis, poison). Opposing or counter-acting putrefaction.
Antrum (Lat. antrum, a cave). The cavity in the upper jaw.
Aorta (Gr. ἀορτή, from ἀείρο, to raise up). The great artery that rises up from the left ventricle of the heart.
Aponeurosis (Gr. ἀπό, from, and νεῦρον, a nerve). A fibrous membranous expansion of a tendon; the nerves and tendons were formerly thought to be identical structures, both appearing as white cords.
Apoplexy (Gr. ἀποπληξία, a sudden stroke). The escape of blood from a ruptured blood-vessel into the substance of the brain.
Apparatus. A number of organs of various sizes and structures working together for some special object.
Appendages (Lat. ad and pendeo, to hang from). Something connected with a part.
Aqueous Humor (Lat. aqua, water). The watery fluid occupying the space between the cornea and crystalline lens of the eye.
Arachnoid Membrane (Gr. ἀράχνη, a spider, and εἰδώς, like). The thin covering of the brain and spinal cord, between the dura mater and the pia mater.
Arbor Vitæ. Literally, “the tree of life”; a name given to the peculiar appearance presented by a section of the cerebellum.