THE THORAX. 201 



downward and inward, toward the median line of the body. (Fig. 140.) They 

 extend from the tubercle of the rib behind to the costo-chondral joint in front. 



The internal intercostal muscles ascend ; their fibres pass inward, upward, 

 and toward the mid-line of the body. They extend from the sternum in front to 

 the angle of the rib behind. 



The osteology of the ribs must be reviewed. A typical rib has : 



1. A head, or articular vertebral extremity. 



2. A neck, or constiction, anterior to the head, extending to the tubercle. 



3. An articular tubercle, articulating with the transverse process. 



4. A non-articidar tubercle, for ligamentous attachment. 



5. A sternal extremity, for articulation with its cartilage. 



6. An outer surface, covered by numerous muscles. 



7. An inner surface, covered by pleura mostly. 



8. A superior border, for muscular attachment. 



9. An inferior border, possessing two lips and a subcostal groove. You must 

 become familiar with all these points on the dry skeleton. 



POSTERIOR KRAXClf OF LA TF.RA L 



ANTKKTOR BRANCH OF LA TKRAL 



<TTA.\i-:ors xi-; 



THE A \TKKIOR PRI- 

 MARY DIVIIO\ 

 OF AN INTERCOS- 

 TAL M-:ilVE 



THE POSTERIOR PR I- 

 MARY IHVISI<>\ HI-' 

 AN INTERCOSTAL 

 NERVE 



<: \.\i:/,/o\ Oh' I'osTKii- 

 IOK ROOT OF SPINAL 

 M-:I; \-K 



ANTERIOR ROOT OF 

 XPIXAL XEUVE 



.s ) '. V r. I Til /; Tl (' GANGLION A XI 

 RA .MI ( 'OMM I \\/( '. I .V /'/> 



FIG. 141. THE INTERCOSTAL NKKVF.S. 



LATERAL CfTANE- 



or.v 



AN INTERCOSTAL SPACE 



An external intercostal 

 * muscle 



An internal intercostal 

 muscle 



COSTO-CHONDRAL JUNCTION 



Iiili'iiinl iixiiuiiHtry 

 artery 



TEHMISrS 0^ IXTKR- 

 rox r.\i. XKR\'K LYIXI; 

 OX POSTERIOR SUR- 

 FM'K (>/ IXTKftl'OST.I I, 

 MI'SfLK. A\l) PASSIXH 

 f\ FROXT OF THK f\- 

 TK I! XA L .WA MM A R Y 

 ARTfJ/lY 



Figure 140 shows the mnscnli infracostales. These muscles arise near the 

 angle of the rib, from the inner surface and lower border ; they are inserted 

 into the second rib above. They are also called subcostals or mnsculi subcostales. 



Intercostal Fascia. Remove every vestige of the pectoralis major, and 

 expose the intercostal muscles. Find a delicate layer of fascia covering the outer 

 surface of the external intercostal muscle. This is the external intercostal fascia. 

 Trace this fascia to the sternum. You can now see, showing through this fascia, 

 the internal intercostal muscle. The internal intercostal fascia covers the inner 

 surface of the internal intercostal muscle. The middle intercostal fascia is be- 

 tween the two intercostal muscles. 



The Intercostal Nerves. Figure 141 represents the cour'se and divisions 

 and relations of an intercostal nerve, such as may be seen in the second, third, 

 fourth, fifth, and sixth intercostal spaces. Students frequently graduate unable 

 to locate properly an intercostal nerve. You are to note the following stages of 

 an intercostal nerve : 



1. -The nerve is formed by an anterior and a posterior root. 



2. The posterior or sensory root has a ganglion. 



'4 



