The sternum and intercostal muscles. 
545 
flat, spongy bone, fixed between the sternal ribs, articulating 
with their cartilages, and serving as a point of support for them. 
It is composed of from seven to nine pieces, united together by 
cartilage. This cartilage is not exchanged for bone even in ex¬ 
treme old age, although many spots of ossific matter are then 
found in it. I have nothing to say of it which bears on physiology 
or pathology; I will therefore content myself with pointing out to 
you the singular cartilaginous appendix anteriorly, in the form of 
the rounded part of the keel of a ship, and which may always 
be felt, and generally seen in the living horse, and is known by 
the name of the point of the breast. It is occasionally injured 
by blows, or by the pressure of the collar. I have known it 
completely chipped or broken off from the sternum; and much 
oftener a kind of tumour has formed on the point of it, which 
has occasionally ulcerated, and proved exceedingly difficult to 
heal. 
The posterior appendix to the sternum is also cartilaginous. 
We call it the ensiform cartilage , although it does not bear much 
resemblance to a sword. It is flat, flexible, yet strong, and serves 
as the commencement of the floor, or support of the abdomen, 
and also as giving origin to some of the abdominal muscles ; and 
a more convenient and better one than they could have had from 
the body of the sternum. 
The Sternum in other Animals. —The ox has no point of the 
breast or trachealian apophysis. The anterior extremity of these 
bones scarcely protrudes beyond the first rib, but it is a great 
deal more moveable than in the horse. The posterior apophysis, 
or appendix, is likewise narrower than in the horse, but longer 
and looser. The interposed cartilage between the bones of the 
sternum become early ossified in the ox. 
In the dog the anterior appendix is curved as in the horse, but 
considerably shorter. In the hog it is shorter than in the dog, 
stronger, soon becoming ossified, and not curved. In the stag 
this ensiform process of the sternum is far more prominent than 
it is in the horse. 
The sternum in birds is a bone of singular development. It 
has a process or spine below of considerable depth for the attach¬ 
ment of the muscles of the breast, and in some of them it is even 
hollowed out for the reception of a part of the trachea. The wild 
swan, whole skeleton is now before you, is an illustration ol 
this. 
The Intercostal Muscles. 
The borders of the ribs arc anteriorly concave, thin, and sharp; 
posteriorly rounded; and presenting underneath a longitudinal 
