Acetabulum (Lat. _acetabulum_, a small vinegar-cup). The cup-shaped cavity of the innominate bone for receiving the head of the femur. Acid (Lat. _acidus_, from _acere_, to be sour). A substance usually sour, sharp, or biting to the taste. Acromion (Gr. ἀκρον the tip, and ᾧμος, the shoulder). The part of the scapula forming the tip of the shoulder. Adam’s Apple. An angular projection of cartilage in the front of the neck. It may be particularly prominent in men. Adductor (Lat. _adduco_, to draw to). A muscle which draws towards the middle line of the body, or of the hand or foot. Adenoid (Gr. ἀδήν, a gland). Tissue resembling gland tissue. Afferent (Lat. _ad_, to, and _fero_, to convey). Vessels or nerves carrying the contents or impulses from the periphery to the center. Albumen, or Albumin (Lat. _albus_, white). An animal substance resembling the white of an egg. Albuminuria. A combination of the words “albumin” and “urine.” Presence of _albumen_ in the _urine_. Aliment (Lat. _alo_, to nourish). That which affords nourishment; food. Alimentary (Lat. _alimentum_, food). Pertaining to _aliment_, or food. Alimentary Canal (Lat. _alimentum_). The tube in which the food is digested or prepared for reception into the blood. Alkali (Arabic _al kali_, the soda plant). A name given to certain substances, such as soda, potash, and the like, which have the power of combining with acids. Alveolar (Lat. _alveolus_, a little hollow). Pertaining to the alveoli, the _cavities_ for the reception of the teeth. Amœba (Gr. ἀμείβω, to change). A single-celled, protoplasmic organism, which is constantly changing its form by protrusions and withdrawals of its substance. Amœboid. Like an _amœba_. Ampulla (Lat. _ampulla_, a wine-flask). The dilated part of the semicircular canals of the internal ear. Anabolism (Gr. ἀναβάλλω, to throw or build up). The process by means of which simpler elements are _built up_ into more complex. Anæsthetics (Gr. ἀν, without, and αἰσθησία, feeling). Those medicinal agents which prevent the feeling of pain, such as chloroform, ether, laughing-gas, etc. Anastomosis (Gr. ἀνά, by, and στόμα, a mouth). The intercommunication of vessels. Anatomy (Gr. ἀνατέμνω, to cut up). The science which describes the structure of living things. The word literally means dissection. 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.