58 OUTLINES OF EQUINE ANATOMY. 



ill all directions ; in the anterior ribs its lower part affords 

 attacliment to serratus magnns, in tlie fourteen posterior 

 ribs to obliquus abdominis externus, in the four or five 

 posterior ribs to obliquus abdominis internus. To about 

 the inferior part of the superior third of the last two ribs 

 a line of prominences extend, one on each rib, from the 

 tubercle of the second ; to this transversalis costarum is 

 attached, while a corresponding superior line of promi- 

 nences runs from the fourth tubercle to meet the former in 

 the sixteenth rib ; it marks out the inferior limit of longis- 

 simus dorsi, and opposite to it the bone makes its most 

 marked curve downwards, which is termed the angle of 

 the rib. Superficialis costarum is attached below the 

 inferior row of prominences. The anterior margin affords 

 attachment to the intercostales externi at its outer edge, 

 superiorly to levatores costarum, at its inner edge to inter- 

 costales interni. In the fourteenth rib a small groove runs 

 along this margin from the head of the bone ; it gradually 

 increases in length in the ribs in front of this, so that in 

 the second, third, and fourth the external margin seems 

 bevelled off from behind forwards, affording extensive 

 surface for attachment. The posterior margin presents a 

 corresponding arrangement on the inner side. It affords 

 attachment to the intercostales in a similar manner to the 

 anterior margin. Towards their inferior extremities the 

 ribs tend to become rounded, the ninth being most so. 

 The posterior ribs assume the character of thin long bones 

 composed of two rounded surfaces meeting by sharp 

 margins. They increase in width from before backwards 

 to the sixth, after which they decrease. In length they 

 decrease from the eighth both backwards and forwards, 

 the first being the shortest. The inferior extremity of the 

 body is continuous with the cartilage of elongation, the 

 union being more or less gomphotic. The cartilage has a 

 considerable tendency to undergo ossification, thus as- 

 suming the normal character of the inferior costa as found in 

 birds ; the bone therefore extends downwards in the centre 

 of the cartilage to a degree varying with the age of the 

 animals. Some of these cartilages are directly attached 

 to the sternum, others indirectly through the medium 

 of their fellows. Those of the first class belong to the 

 first eight ribs, which therefore are said to be true ribs, 

 behind these, on each side, are generally ten false ribs^ 



