ANATOMY OF THE HOKSE. 
107 
head. 3. The tubercle, the prominence behind the head, at the 
root of the neck, which has a flat smooth surface for articu¬ 
lation with the transverse process of the hinder vertebra con¬ 
nected with the head. 4. In front of the tubercle, running 
across the back of the neck, is a groove, along which make their 
exit branches from the intercostal vessels and nerves. The in¬ 
ferior or sternal extremity swells a little in volume, and is of 
less compact or more porous texture than the bone above : it is 
terminated by an oval roughened depression ; from this takes 
root the cartilage of the rib, which thence proceeds at a more or 
less obtuse or roundbd angle towards the sternum. 
Surfaces. The external is convex and more or less uneven. 
The ribs do not form regular arches; they project outwards 
from the spine, and then curve suddenly downwards, the poste¬ 
rior ones at the same time inclining backwards : the place where 
the rib commences its descent, the most convex or crooked part, 
is named its angle. In all the long ribs this surface anteriorly 
is more or less grooved for the attachment of the external inter¬ 
costal muscles.—The internal surface is uniformly concave, 
smooth, and polished. It is lined by the pleura. 
Borders. With the exception o^^he first and last ribs, the 
anterior borders are thin and sharp; the posterior, obtuse and 
rounded: the former give attachment to the intercostal mus¬ 
cles ; the latter, along the upper half however only, present 
grooves in which run the intercostal vessels and nerves. 
Peculiarities. The first is the shortest and thickest of the 
ribs ; its upper part is rounder, and its lower broader and more 
expanded than any other : it is but little and irregularly arch¬ 
ed, and the concavity of its arch is turned directly forwards. 
The second is a remarkably straight rib, being only curved in 
its neck. From the second the ribs progressively increase in 
breadth to the seventh, in length to the ninth, and in curvature 
to the very last; the eighteenth being in proportion to its length 
the most crooked rib: from the tenth, the ribs grow shorter, 
narrower, and more obtuse or rounder in their borders. The 
posterior differ also from the anterior ribs in being curved 
throughout their entire length ; whereas the former are only 
very perceptibly bent at their angles. In the eighteenth, and' 
sometimes in the seventeenth rib, the articulatory surface of 
the tubercle is confounded with that of the head, and the 
neck is wanting. 
The Cartilages of the Ribs, properly so called in 
the young subject, receive depositions of osseous matter as the 
animal advances in life, and at length acquire rather the charac¬ 
ter of spongy fragile bones than cartilage. They correspond in 
