50 THE CAT. [chap. hi. 



portion of the trunk in the middle line, but it is very much smaller 

 and less complex than is the backbone. It is flattened from above 

 downwards, but still more so from side to side, and consists of a chain 

 of eight bones, called sternehra>., about fifteen or sixteen times as long 

 as broad, but its width varies slightly at intervals throughout its 

 ■whole extent. 



The sternum is connected on each side with the cartilages {ca) of 

 the first nine ribs, one cartilage on each side being attached to each 

 successive pair of sternebra) at their junction, as well as to the side 

 of the manubrium and the hinder end of the seventh sternebra. 



The first sternebra, which ends anteriorly in a laterally compressed 

 pointed process {p), is called the manuhrium, or presternum, and 

 extends forwards in front of the insertion of the cartilage of the first 

 rib. The second part (or the bod// of the sternum) is made up of all 

 the other six sternebra) together. The third part (x) is the xiphoid, 

 or ensiform, process, which varies in shape in different individuals, 

 and long remains cartilaginous. The hinder end of the manubrium 

 affords a surface for the attachment of the second costal cartilage. 



The first sternebra of the hod// completes the surface for the 

 second rib. The notches for the third, fourth, fifth, sixth and 

 seventh ribs are situated at the lines of junction of the sterncbrse of 

 the body of the sternum — as before mentioned. The notches for the 

 eighth and ninth rib cartilages are placed close together at the 

 hinder end of the seventh sternebra (see below, Fig. 78, B,/'). 



This xiphoid cartilage projects freely backwards, tapering towards 

 its generally more or less expanded and fan-shaped distal end (c). 



§ 16. The RIBS {costce) are long, slender, curved bones, which 

 extend obliquely downwards from the spinal column, and end below 

 in cartilaginous prolongations called costal cartilages. Some of these 

 join the sternum by their cartilages (Fig. 24, ca), and others do not. 

 There are thirteen libs on each side. The nine anterior ribs on 

 each side are called " true ribs," and join the sternum by their 

 cartilages. The four hinder ribs do not join the sternum, and arc 

 therefore called " false ribs." The ribs generally are curved at 

 first (starting from their attachments to the vertebral centra) out- 

 wards and a little upwards, then backwards, and outwards and 

 much downwards. 



Taldug the sixth rih as a type, the following points may be 

 noted : its proximal or upper and inner end is thickened, and is 

 called the capitiiluni, or head, of the rib (c), and it is this which 

 joins the capitular surfaces of the fifth and sixth dorsal vcrtebne by 

 two corresponding oblique articular surfaces, with a ridge between. 

 The i)art of the rib next to the head is termed the neck (ii), and 

 this short portion terminates at what is called the tuhcrcuhtm (f), or 

 tubercle of the rib. This is a rounded prominence on the hinder 

 border of the bone. It looks upwards, and presents a smooth 

 surface for articulation with the transverse process of the sixth 

 dorsal vertebra ; outside this smooth prominence is a rough surface 

 of bone. The neck of the rib is narrower than is the fii'st part 



