110 
ANATOIVIY OF THE HORSE. 
/ 
THE HUMP-BONE. (OS SACRUM.) 
' Situation, At the superior part of the pelvis, continued from 
the vertebral chain between the ossa ilia. 
Figure. Resembling the lumbar portion of the spine, from 
which it declines with a slight bend, presenting a convexity 
externally, a concavity internally, thereby augmenting the area 
of the pelvic cavity. 
Division. Into two surfaces, two borders, a base, and an 
apex. 
Superior Surface. Very irregular. Presenting, 1st. On the 
mesian line, five considerable eminences, corresponding to the 
lumbar spines, from which they differ in sloping in an opposite 
direction, in increasing in breadth, while they diminish in 
length, from first to last. 2ndly. Laterally, two superficial 
grooves, pierced by the four superior sacral foramina, through 
which pass out the superior sacral nerves. 
Inferior Surface. Regular, smooth, and slightly concave. It 
presents—Four transverse lines of demarcation, denoting the 
original division of the bone into four separate pieces. These 
are bounded laterally by two superficial grooves, pierced by four 
pairs of inferior sacral foramina, through which make exit the 
corresponding sacral nerves. 
Lateral Surfaces. Thick anteriorly, growing thin posteriorly, 
and presenting slight protuberances, corresponding to the ver¬ 
tebral transverse processes, which serve for the attachment of 
the sacro-iliac ligaments. 
Base. Composed of a middle and two lateral parts. ' The 
middle presents a convex articulatory surface, transversely oval, 
for adaptation to the last lumbar vertebra; surmounted by two 
articulatory processes, between which are received the two last 
of that name of the loins; and having on its sides two notches 
of conjugation for the last pair of lumbar nerves. The lateral 
or anterior transverse processes, broad, thick, and projecting, 
and triangular in figure, point forwards and upwards as well as 
outwards : superiorly, they have two surfaces of articulation for 
the ossa ilia ; anteriorly, two others which unite with the last 
transverse processes of the loins. 
Apex. Presents also an oval surface, which articulates with 
the foremost bone of the tail; having on its sides 'two notches, 
lor the fifth pair of sacral nerves; and, farther removed out¬ 
ward, two little posterior transverse processes. 
The Sacral Canal for the spinal marrow is triangular in 
figure, and gradually contracts its diameter from before back¬ 
wards. 
