510 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



cesses of the two or three lower cervical vertebrae to the outer surface of the 

 second rib. 



The serrati postici superiores aid in fixing the second ribs and raise the third, 

 fourth, and fifth ribs. The muscles pass from the ligamentum nuchse and the 

 spines of the seventh cervical and first two or three dorsal vertebrae to the upper 

 borders of the second, third, fourth, and fifth ribs, beyond their angles. 



The levatores costarum breves consist of twelve pairs which pass from the 

 tips of the transverse processes of the seventh cervical and first to the eleventh 

 dorsal vertebra? downward and outward, each being inserted between the 

 tubercle and the angle of the next rib below. Those arising from the lower 

 ribs send fibres to the second rib below (levatores costarum longiores). They 

 assist in the elevation and eversion of the first to the tenth ribs, inclusive, and 

 co-operate with the quadrati lumborum and the serrati postici inferiores to 

 draw the lower ribs backward. 



The functions of the intercostales have been a matter of dispute for centu- 

 ries, and the problem is still unsettled. For instance, Galen looked upon the 

 external intercostals as being expiratory. Vesalius asserted that both the 

 external and the internal intercostals are expiratory, while Haller expressed 

 the opposite belief. Hamberger and Hutchinson regarded the external inter- 

 costals and the interchondrals as being inspiratory, and the interosseous portion 

 of the internal intercostals as being expiratory. Finally, Landois believes that 

 while the external intercostals and the interchondrals are active during inspira- 

 tion, and the interosseous portion of the internal intercostals during expiration, 

 their chief actions are not to enlarge nor to diminish the volume of the thoracic 

 cavity, but to maintain a proper degree of tension of the intercostal spaces. 

 Each view still has its adherents. 



The actions of the intercostal muscles are generally demonstrated by means 

 of rods and elastic bands arranged in imitation of the ribs and the origins and 

 insertions of the muscles, or by geometric diagrams. The well-known model 

 of Bernouilli consists of a vertical bar representing the vertebral column, upon 

 which bar move two parallel straight rods in imitation of the ribs (Fig. 134). 

 If the rods be placed at an oblique angle and a tense rubber band (a, b) be 

 affixed to represent the relations of the external intercostals, the rods will be 

 pulled upward and the space between them will be widened. The interchon- 

 dral portion of the internal intercostals bears the same oblique relation to the 

 costal cartilages, and theoretically should have the same action. The action 

 of the interosseous portion of the internal intercostals is demonstrated in this 

 way : If the rubber band be placed at right angles to the rods (Fig. 135, a, 6) 

 and the rods be raised to a horizontal position, the rubber is put on the stretch 

 (c, d), so that when the rods are released they will be pulled downward by the 

 elastic reaction of the rubber. This last demonstration has been held to indi- 

 cate that during inspiration the interosseous portion of the internal intercostals 

 is put on the stretch and in an oblique position, and therefore in a relation 

 favorable for eifective action during contraction. The ribs, however, differ 

 essentially from such a model in the fact that they are curved bars, that their 



