33-4 THE HORSE. 
last they become more curved and short. In the seventeenth and eighteenth 
the articulatory surface of the tubercle becomes confounded with that of 
the head, and the neck is wanting. (See 2,3, B. Fig. 21.) 
THE STERNUM, OR BREAST-BONE 
THE sTERNUM, which forms the inferior boundary of the thorax (see 
page 308), forms in the adult one long keel-like bone, of a spongy or 
cellular nature, more or less divided by cartilage ; but in the embryo it. 
Fia. 22.—ProFiLe View or STERNUM (BREAST-BONE). 
- 1.1. &c. Pits for attachment of costalcartilages. 3. 3. Posterior extremity with its ensiform car- 
2. 2. Anterior extremity ending in cariniform tilage. 
cartilage. 
1 
like the sacrum, is made up of distinct pieces, six or seven in number. 
Anteriorly the breast-bone is prolonged in a manner resembling the keel 
and figurehead of a ship, being clothed with cartilage, which is hence 
called cariniform (carina, a keel) (2, 2, Fig. 22). Posteriorly it terminates 
also in a cartilage of a thinner and more flexible form, and called, from its 
resemblance to a sword, ensiform (ensis, Lat. sword) or xiphoid (Eéoc, 
Gk. sword). 
THE SIDES are occupied above by the cavities for the insertion of the 
costal cartilages, and below by a rough surface, to which the fibres of the 
pectoral muscles are attached. The superior face forms a very lengthened 
isosceles triangle, having its apex forward. It is slightly hollowed from 
before backwards. 
THE THREE ANTERIOR DIVISIONS of the sternum present broad lateral 
surfaces ; the three pusterior have projecting sides inclining downwards, 
and forming the boundaries between the inferior surface and the sides. 
The ribs are received into cavities in the cartilage existing between the 
separate bones, the last posteriorly having, however, an additional pit in 
its middle for the cartilage of the eighth rib. 
SCAPULA. BLADE-BONE, OR SHOULDER-BLADE. 
INTERVENING BETWEEN the thorax and the fore extremity, and present- 
ing large surfaces for the attachment of muscles to connect these two 
parts of the skeleton, is the scapula or shoulder-blade. It is a triangular 
flat bone, and lies obliquely on each side of the anterior part of the 
thorax, with its apex looking downwards and forwards, and its base 
upwards and backwards (see page 308). 
IT prREsENTS three fossze, three borders, and three angles; in addition 
to which there are the spine, the coracoid process, and the glenoid cavity. 
