AN ARMED QUADRUPED. 229 



sheath of nerves, as they pass from the encephalic cavities. 

 Its chief uses seem to be to envelop and, in some measure, 

 protect the brain, and to secrete a fluid for the purpose of 

 keeping it in a state best adapted for the performance of its 

 functions. 



ARE'OLA. A diminutive of 'area/ Anatomists understand by 

 areolae the interstices between the fibers composing organs, 

 or those existing between laminae, or between vessels which 

 interlace with each other. 



ARGEN'TI NITRAS. Nitrate of silver ; lunar caustic. The vir- 

 tues of nitrate of silver are tonic and escharotic. It is given 

 in chorea, epilepsy, &c.; locally, it is used in various cases as 

 an escharotic. Dose, gr. 1-8 to gr. 1-4, in pill, three times 

 a day. 



ARMADIL'LO. (So called from being protected or armed by a 

 scaly covering like 'the plate armor of the middle ages.) A 

 genus of South American quadrupeds, belonging to the order 

 of edentata, and characterized by a defensive armor of small 

 bony plates, covering the head and trunk, and sometimes the 

 tail. Brands. 



ARTICULA'TTON. The union of bones with each other, as well 

 as the kind of union. Articulations are generally divided 

 into two kinds movable and immovable. The articulations 

 are subject to a number of diseases, which are generally some- 

 what severe; they may be physical, as wounds, sprains, lux- 

 ations, &c., or they may be organic, as ankylosis, extraneous 

 bodies, caries, rheumatism, gout, &c. 



AT'ROPHY. Progressive and morbid diminution in the bulk of 

 the whole body or of a part. Atrophy is generally symp- 

 tomatic. Any tissue or organ thus affected is said to be 

 ' atrophied.' 



AURIC'ULAR. (The ear.) That which belongs to the ear, espe- 

 cially the external ear. 



B. 



BATRA'CHIA. An order of reptiles including toads, frogs, and 



salamanders. Brande. 



One of the five great classes into which vertebrate animals 



are usually divided, though some writers have reduced the 



class to the rank of an order of reptiles, a class with which 



