THE Ml'SCl.i -':;7 



3. External Intn-<-*t1x. (Fig. 104, 68.) 



Situation Form. Thcso muscles fill the spaces between the ribs, but 

 do not descend beyond their inferior extremities; they, therefore, do not 

 occupy the intervals between the cartilages. They are flattened, fle.-hy 

 blinds, gradually diminishing in thickness from above to below. 



Structure Attachments. Each intercostal muscle is composed of a 

 snics of muscular fasciculi, intermixed with numerous aponeurotic fibres, 

 both of which pass obliquely backwards and downwards, from the posterior 

 Ix.rdor of the preceding to the external face of the succeeding rib. 



/.' Intinns. They respond, outwardly, to the different muscles applied 

 against the thoracic walls ; inwardly, to the internal iutercostals. 



4. Internal Intercostal*. (Fig. 106, 16.) 



Those are placed at the internal face of the preceding, which they exactly 

 repeat with regard to their general form, but from which they differ in the 

 following points : 



1. Very thick between the costal cartilages, these muscles are reduced 

 at tho upper part of the intercostal spaces to a thin aponeurotic layer, 

 supported only by some fleshy fibres. They therefore gradually diminish 

 in thickness from below upwards. 



2. Their fasciculi are less tendinous than those of the external inter- 

 costals, and are carried obliquely forward and downward, from the anterior 

 border of tho 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 

 cadi other like the letter X. 



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

 tin costal pleura. 



Actii'it <>f tlic intercf'Stal 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 

 >ul>ject than on this. M. Berard, who has summed up the elements of the 

 discussion with the greatest judgment, considers the external intcrcostals as 

 inspiratory muscles, and the internal ones also as inspiratory by those 

 fasciculi which occupy tho spaces between the costal cartilages ; the 

 reiiiiiinder, the majority, are expiratory. 



n. 



*. -Traii.-vt rso-costales Girard. (Levatores contarum PerciralL) 

 Small, tliit. triangular, muscular and tendinous fasciculi, constituting. 



it might be said, the heads of the external intercostal*, from which they are 



scarcely distinguishable in the tit>t and la<t costal intervals. 



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

 : d backwards and outwards, gradually expanding, to terminate on the 



\t' rnal face of tho one or two ribs which succeed their fixed insertion. 



Outwardly, they respond to tho ilio-spinalis ; inwardly, to tho external 



interoostals. 



The supcrcostals draw tho ribs forward, and are consequently iuspiratory 



niuscli s, 



6. Trianfjularin of tin- Shnnnn. 

 Synonym*. Stcrnalia Uonnjclat. Stomo-oostalia Cimr I. The fonto-owtolM of 



'.all. :il 



