68 



PRACTICAL ANATOMY. 



subclavian. It passes through the foramina in the transverse processes of the 

 cervical vertebrae, except the lower two, and through the foramen magnum, in 

 the occipital bone, to assist the internal carotid artery in forming, by anasto- 

 mosis, the circle of Willis. The artery is attended by a sympathetic plexus of 

 nerves from the inferior cervical ganglion. The artery is found lying in the 

 vertebral groove, at the junction of the lateral mass and posterior arch of the 

 atlas in the suboccipital triangle, at the base of the skull. This triangle is 

 bounded by the superior and inferior oblique and rectus capitis posticus major 

 muscles. The roof of the triangle is the complexus muscle. 

 Branches of the vertebral artery are as follows : 



1. Muscular branches to the deep muscles of the neck. 



2. Lateral spinal arteries to the spinal cord and meninges ; the bodies of the 

 vertebrae also receive blood from these branches. 



Scalenus anticus muscle 



Deep cervical branch 



FIRST DORSAL NERVE 



FIRST INTERCOSTAL 

 NER VE 



Subclavian artery 



SECONH I \TKRCOSTAL 



Anterior intercostal 



artery 



THIRD INTER- 

 COSTAL NERVE 



Anterior intercostal 

 artery 



Intercostal vessels qf 

 third space 



SYMPA THE TIC 

 SER VE 



INFERIOR CERVI- 

 CAL GANGLION 



} Superior intercostal 

 artery 



Arter ia aberrant 



Branch from first aortic 

 intercostal 



Arteria aberrant 



Fint aortic intercostal 



artery 



Second aortic intercostal 

 artery 



Intei costal vessels of fourth space 



FIG. 39. SCHEME OF THE SUPERIOR INTERCOSTAL ARTERY. 



3. Anterior and posterior spinal branches that may be well seen when y( 

 dissect the cord. 



4. Posterior inferior ccrcbellar arteries. These are the largest arteries given off 

 from the vertebral. They will be studied when we consider the structures seen 

 on removing the brain. The two vertebral arteries unite, within the cranium, to 

 form the basilar artery. This artery will be studied when you remove the 

 brain. 



The transversalis colli is a branch of the thyroid axis. It gives off the 

 posterior scapular artery, by which collateral circulation is established with the 

 subscapular branch of the axillary artery in cases of ligation of the third stage 

 of the subclavian artery. (Figs. 38, 39, and 40.) 



The scaleni muscles are three in number. You have already studied their 

 insertion into the first and second ribs. You will now review the relation be- 





