'2i)0 VOCA'UULAKY. 



parts by areolar tissue. Its inner surface covers the bones, 

 wliose depressions it accurately follows. It is united to the 

 bone by small fibrous prolongations, and especially by a pro- 

 digious quantity of vessels, which penetrate their substance. 

 It unites the bones to the neighboring parts, and assists in 

 their growth, either by furnishing, at its inner surface, an 

 albuminous exudation, which becomes cartilaginous and at 

 length ossifies, or by supporting the vessels which penetrate 

 them to carry the materials of their nutrition. 



Petrous, Resembling stone ; having the hardness of stone. 



Phlegmon. Inflammation of the areolar texture, accorfepanied 

 with redness, circumscribed swelling, increased heat and 

 pain, which, at first, is tensive and lancinating and afterward 

 pulsatory and heavy. It is apt to terminate in suppuration. 



PiA Mater (tender mother), so named because it nourishes the 

 nerve-centers. The innermost covering of the brain and 

 spinal cord ; a fine plexus of blood-vessels, dipping into the 

 brain's convolutions, forming the velum interpositum in the 

 third and the choroid plexus in the fourth ventricle. A 

 small part (over the crura and pons) is not very vascular, but 

 tough and fibrous, while that of the spinal cord, with Avhich 

 it is intimately connected and of w^iich it is the neurilemma, 

 is still less vascular. It is partly composed of longitudinal 

 fibrous bundles, and is abundantly supplied with nerves and 

 lymphatics. The tunica vasculosa of the testes is also called 

 pia mater. Johnson's JSf. JJ. Cyc. 



PiTU'iTARY. Concerned in the secretion of muscus or phlegm. 



Pituitary Membrane. The mucous membrane wMiich lines 

 the nasal fossa?, and extends to the cavities communicating 

 with the nose. It is the seat of smell. 



Plas'ma. See 'Liquor Sanguinis.' 



Pleistocene. A term used to denote the newest tertiary de- 

 posits. JoJinsoji's N. JJ. Cyc. 



Pli'ocene. In geology, the term applied to the most modern 

 of tertiary deposits, in w^hich most of the fossil shells are of 

 recent species. Lyell. 



With regard to animal life, the Pliocene continues the con- 

 ditions of the Miocene, but with signs of decadence. The 

 Pliocene was terminated by the cold or Glacial period, in 

 which a remarkable lowering of temperature occurred over 



