298 THE MUSCLES. 



2. Their fasciculi are less tendinous than those of the external intercostals, 

 and are carried obliquely forward and downward, from the anterior border of 

 the posterior rib to the posterior border and internal face of the rib in front ; 

 so that the fibres of the external and internal intercostals cross each other like 

 the letter X. 



3. Outwardly, they respond to the external intercostals ; inwardly, to the 

 costal pleura. 



Action of the intercostal muscles. — The function of these muscles has been for 

 a long time, and is even now, much discussed ; and it may be said that there 

 were never, perhaps, more diverse or contrary opinions given on any subject 

 than on this. Berard, who has summed up the elements of the discussion 

 w'ith the greatest judgment, considers the external intercostals as inspiratory 

 muscles, and the internal ones also as inspiratory by those fasciculi which occupy 

 the spaces between the costal cartilages ; the remainder, the majority, are 

 expiratory. 



4. Levatores Cost arum. 



Synonyms. — Trans verso-costales — Girard. 



Small, flat, triangular, muscular, and tendinous fasciculi, constituting, it 

 might be said, the heads of the external intercostals, from which they are 

 scarcely distinguishable in the iirst and last costal intervals. 



They arise from the transverse processes of the dorsal vertebrae, and are 

 directed backwards and outwards, gradually expanding, to terminate on the 

 external face of the one or two ribs which succeed their fixed insertion. Out- 

 wardly, they are in contact with the longissimus dorsi; inwardly, with the 

 external intercostals. 



The levatores costarum draw the ribs forward, and are consequently inspiratory 

 muscles. 



5. Triangularis Sterni. 



Synonyms. — Sternalia — Bourgelat. Sterno-costalis — Girard. (The sterno-costales of Per- 

 civall, and sterno-costalis of Leyh.) 



Form — Situation. — This muscle, flattened above and below, elongated from 

 before to behind, and dentated at its external or superior border, is situated in 

 the thoracic cavity, above the sternum and the cartilages of the true ribs. 



Attachments. — It is fixed, by its internal border, on the superior face of the 

 sternum, to the ligamentous cord which circumscribes it outwardly. It has its 

 movable insertion on the cartilages of the sternal ribs, the first excepted, by 

 means of digitations from its external border. 



Structure. — It is formed of strongly aponeurotic muscular fasciculi, which 

 are directed from the internal to the external border. 



Relations. — Inwardly, with the pleura ; outwardly, with the cartilages to 

 which it is attached, the internal intercostals, and the internal thoracic vein and 

 artery. 



Action. — ^The triangularis of the sternum concure in expiration, by depressing 

 the costal cartilages. (Leyh asserts that if the fixed point be the sternum, this 

 muscle pulls the ribs forwards, and so widens the thorax ; but if the fixed point 

 is the ribs, the sternum will be raised and the thoracic space diminished.) 



