742 AN URINARY CALCULUS AND ITS EXPULSION. 
than the upper, is remarkably smooth, and several places are 
almost polished. The lower division of the borders are 
slightly roughened, but not beaded, simply corresponding 
with the asperities of those parts which have been in partial 
apposition to the mucous surface of the bladder. 
One of the angles, which would appear to have rested in 
the fundus of the bladder is less obtuse, but smoother than 
the remaining tw^o, which w^ere only semi-contiguous and 
posteriorly placed, their aspect being uneven and rough. 
General Character .—Its colour externally, when dry, 
varies from that of a pale yellow or light clay tint to that of a 
brownish-red, the former, however, preponderating. Exposure 
has considerably bleached the specimen. 
A horizontal section (through its greatest circumference), 
exposing the largest amount of inner surface, presents two 
appearances, which, for the sake of description, may be called 
marginal and central. 
The former is dense, hard, laminated, and shell-like, and 
has been rendered smooth and semi-polished by the saw. It 
measures from half to one and half lines broad, and is com¬ 
posed of three principal layers, which, however, do not main¬ 
tain themselves entire throughout the circumference; but, 
after preserving an uninterrupted position for half the distance, 
the outer layer ceases, and reappears at irregular intervals. 
The remaining parts of the marginal surface are made up 
of the inner layer, which in some places is surmounted by the 
middle one. 
These layers are of two shades. The middle one, which is 
narrow and undulating, is very much darker than the two 
wider ones which confine it, probably due to a greater 
admixture of organic matter. 
In some parts the difference in colour is less defined, but 
the darker hue pervades the whole. In whatever direction 
the calculus is fractured the same features are preserved. 
The latter (central), with one or two exceptions, shows a 
tolerably uniform colour, a light gravelly brown. Its surface, 
whether cut or fractured, is uneven, coarse, and much less 
condensed than the marginal crust. Its substance is friable, 
and resembles fine gravel massed together. 
Looking upon the cut surface, an appearance of irregular 
radiation is definable, and there are slight evidences of con¬ 
centric rings, botli features originating in a dark body, which 
is a carbonaceous looking mass about the size of a large horse- 
bean, and forms the nucleus around wdiich the whole calca¬ 
reous matter was constructed. It holds a position not quite 
central to the stone, and is of a deep chocolate colour, soft. 
