68 



PRACTICAL ANATOMY. 



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

 cervical vertebra;, 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 \Villis. 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 sitboccipital 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 

 vertebra; also receive blood from these branches. 



Scalenus anticus muscle 



l}?ep cervical branch 



FIRST DORSAL NERVE 



FIRST INTERCOSTAL 

 NERVE 



Siibctavian artery 



SECOND INTERCOSTAL 

 KEBVE 



Anterior intercostal 



nrtery 



THIRD INTER- 

 COSTAL NERVE 



Anterior intercostal 



artitrg 



Internal mammary \'. 

 artery 



Intercostal ressfls o/ 

 third space 



SYMPA TI1ET1C 

 NEK VE 



INFERIOR CERVI- 

 CAL GANGLION 



{Superior intercostal 

 j artery 



Arteria aberrant 



Branch from first aortic 

 in/ercus/al 



Arteria aberrant 



First aortic intercostal 



artery 



Second aortic intercostal 

 artery 



Intel costal vessels oj'Jou/ th sjiace 

 FlG. 39. SCHEMK OF THE SUPERIOR INTERCOSTAL ARTERY. 



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

 dissect the cord. 



4. Posterior inferior cercbcllar 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- 



