M E A 



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MED 



greater and less. The mean of any 

 number of unequal quantities is 

 equal to their sum divided by their 

 number. For instance, the mean 

 between two unequal quantities is 

 equal to half their sum. Mrs. 

 Somerville. 



MEAG'BE. A term used in mineralogy 

 relating to the touch or feel of a 

 mineral. Chalk is said to be 

 meagre. 



MEANDBI'NA. Brain-stone ; brain- 

 coral. Madrepores in which the 

 laminae assume a meandering di- 

 rection are called meandrinae. Me- 

 andrinae are large hemispherical 

 corals, having their surface covered 

 with serpentine ridges and de- 

 pressions, resembling the convo- 

 lutions of the cerebrum, or brain, 

 from which circumstance they have 

 been called brain- stone. " On the 

 convex side," says Mr. Parkinson, 

 "are excavated, open, winding, 

 ambulacrae, lamellated on each 

 side. The lamellae are transverse 

 and parallel, adhering on each side 

 of hillock-shaped ridges. The la- 

 mellated ridges occupy the inter- 

 stices of the tortuous vallies which 

 hold the polypes and thus separate 

 them. Fossil meandrinae are found 

 both in the cretaceous and oolite 

 series." 



(Lat.) A passage, as that 

 leading to the ear, called the 

 meatus auditorius, &c. 

 MEDIAL ORDEE. A term proposed by 

 the Rev. J. Conybeare for that 

 assemblage of rocks which contains 

 not only the great coal deposit 

 itself, but also the limestone and 

 sandstone on which it reposes. 

 " This series of rocks," says Dean 

 Conybeare, " is by some geologists 

 referred to the flcetz, and by others 

 to the transition class of the 

 Wernerians. We have preferred 

 instituting a particular order for 

 its reception, a proceeding justified 

 by its proportional importance in 

 the geological scale, its peculiar 



characters, and the many incon- 

 veniences arising from following 

 either of the above conflicting 

 examples. For this order we have 

 proposed the name of Medial, 

 wishing to adopt an appellation 

 entirely free from theory ; and 

 indicating only the central position 

 of this groupe in the five-fold 

 division of the geological series 

 which results from assigning to it 

 a separate class." 



MEDTJ'LLA. (medulla, the marrow, 

 Lat.) 



1. In botany, the pith of plants. 



2. The marrow in the cavities of 

 bones. 



ME'DTTLLARY. (medullaris, Lat.) 



1. Eclating to the brain, or to the 

 marrow. The medullary substance 

 composes the greater part of the 

 brain, spinal marrow, and nerves. 



2. In botany, relating to the pith 

 of plants. 



MEDTJ'LLIN. A name given by Dr. 

 John to the porous pith of the sun- 

 flower. 



MEDT/SA. A genus of marine mol- 

 luscous animals belonging to the 

 class Acalepha. The medusce ap- 

 proach nearly to the fluid state, 

 appearing like a soft and transpa- 

 rent jelly, which by spontaneous 

 decomposition after death, or by 

 the application of heat, is resolved 

 almost into a limpid watery fluid. 

 The usual form of a medusa is that 

 of a hemisphere, with a marginal 

 membrane, like the fold of a man- 

 tle, extending loosely downwards 

 from the circumference. 



Medusce are met with of very 

 various sizes; the larger abound 

 in the seas around our coasts, but 

 immense numbers of the more 

 minute, and often microscopic, 

 species occur in every part of the 

 ocean. In some parts of the Green- 

 land seas the number of Medusae is 

 so great, that in a cubic inch, taken 

 up at random, there are not fewer 

 than 64. In a cubic foot this will 



