142 MAMMALIAN ANATOMY 



to the fifth it is oval, on the fifth and sixth circular, at the seventh 

 it begins to be oval again and to extend upon the neck of the rib, and 

 when the tenth is reached it has become oblong or pear-shaped, and 

 almost touches the head. 



The shaft is straighter in the first two and more curved in all the 

 rest. It is more cylindrical in the first rib, and the terminal surface 

 on the sternal end is almost circular ; from the second to the eighth 

 the sternal part of the shaft is flattened, and the terminal surface is 

 transversely narrow ; from the eighth to the end of the series the body 

 of the rib is more cylindrical, and the terminal surface on the sternal 

 end is less oval and more circular. 



The angle of the rib is absent from the first, and is well marked 

 from the second to the sixth. A secondary tubercle at the lower end 

 of the superior crest of the rib and above the angle appears on old, 

 strongly developed ribs from the fourth to the eleventh. The tubercle 

 for the attachment of the slips from the erector spiuse muscle marks 

 approximately the angle, and is present in old bones from the second 

 to the seventh inclusive. 



Nomenclature. The Latin for rib is costa ; the German, die 

 R'uppe ; the French, le cote. 



Determination. The head is on the vertebral end; the tubercle is 

 on the dorsal border, and its articular surface faces to a greater extent 

 toward the tail than toward the head. Therefore, if the head be held 

 upward and the concavity of the rib toward the student, the articular 

 surface of the tubercle and the inner surface of the body will be on 

 the side, either right or left, to which the bone belongs. 



Muscular Attachments. The following are the principal 

 muscles attached to the ribs : 



The serratus magnus, to the cephalic-lateral surface of the first 

 nine ribs, at, or dorsal to, the junction of the rib and the cartilage ; 

 the scalenes, to the cephalic-lateral surface of the first rib, and to 

 the ventral-cephalic border of the third, fifth, seventh, and eighth 

 ribs, near the serratus magnus ; the external oblique, to the cephalic- 

 lateral surface of the last nine ribs (on the fifth to the ninth just 

 dorsal to the attachment of the serratus magnus; on the tenth to the 

 thirteenth progressively* more dorsal) ; the internal oblique, to the 

 dorsal-caudal border of the last five ribs ; the transversalis, to the 

 medial surface of the last five costal cartilages ; the serratus posticus, 



