560 



THE BLOOD-VASCULAR SYSTEM 



side is the scalenus anterior. It gives off as a rule no branch in this part of its course. Occa- 

 sionallj', however, a small branch passes into the foramen tranversarium of the seventh cervical 

 vertebra. 



The second or vertebral portion. — As the artery passes through the foramina transversaria, 

 it is surriunded by a plexus of veins and bj' branches of the sj'mpathetic nerve. The cervical 

 nerves lie behind it. Between the transverse processes it is in contact with the intertransverse 

 muscles. 



The third or occipital portion. — The artery here lies in the suboccipital triangle, bounded 

 by the superior obhque, inferior obhque, and rectus capitis posterior major muscles. As it 

 winds round the groove on the atlas, it has the rectus capitis laterahs, the articular process, 

 and the posterior occipito-atlantoid membrane in front of it; the superior oblique, the rectus 

 capitis posterior major, and the semispinalis capitis (complexus) behind it. Separating it 

 from the arch of the atlas, is the first cervical or suboccipital nerve. 



The fourth or intracranial portion extends from the aperture in the dura mater to the 

 lower border of the pons, where it pierces the arachnoid and unites with its fellow to form the 

 basilar arterj'. It here winds round from the side to the front of the medulla, lying in the 



Fig. 458. — Scheme of the Left Vertebral Artery. (Walsham.) 

 The internal jugular and vertebral veins are hooked aside to expose the artery. 

 Right posterior cerebral ^ , 



artery 

 Left posterior cerebral 

 artery 

 Basilar artery 



Basilar part, occipital 

 bone 



Intracranial portion of verte- 

 bral artery 

 Rectus capitis lateralis muscle 



First cervical nerve 

 Commencement of vertebral 

 vein 



Second cervical nerve 



Vertebral plexus of veins 



Third cervical nerve 



Vertebral portion of vertebral 

 artery 

 Fourth cervical nerve 



Vertebral plexus of veins 



Fifth cervical nerve 



Sixth cervical nerve 



Inferior thyreoid artery 



Longus colli muscle 



Cervical portion of vertebral 



artery 



Internal jugular vein, hooked a 



little aside 



Vertebral vein, cut 

 Subclavian artery 



Right and left superior 

 cerebellar arteries 



Occipital bone 



Rectus capitis posterior 

 minor muscle 



Occipital portion of vertebral artery 



Descending branch of occipital artery 



Semispinalis colli muscle 



Deep cervical artery 



Scalenus anterior muscle, cut 



Thyreo-cervical trunk, hooked a little 

 aside 



Subclavian vein 



vertebral groove on the basilar part of the occipital l)one. In this course it passes beneath 

 the first process of the ligamentum deiiticulatum, and between the hypoglossal nerve in front, 

 and the anterior roots of the suboccipital nerve behind. 



Branches of the Vertebral Artery 



The first part of the vertebral artery gives no branches. The second and third 

 parts give off muscular branches to the semispinalis and posterior recti and oblique 

 niusch.'S. The second part also gives off five or six, (1) Spinal branches. The 

 fourth part giv(;s off the following: (2) Posterior meningeal; (3) posterior spinal; 

 (4) anterior spinal; and (5) posterior inferior cerebellar. 



(1) The spinal branches [rami spiiiides] run through the intervertebral foramina into the 

 vertebral canal, and there divide into two branches: one of which ramifies on the backs of 

 the bodies of the cervical verte))ra'; while the other runs along the spinal nerves, supplies the 

 cord and its membranes, und ana.stomoscs with the arteries above and below. 



(2) The meningeal lianius mcningeiisl is a small brancli given off as the vertebral artery 

 pierces tlie diua mater to enter the craniuiii. It siipph(;s the bone and dura mater of the 

 posterior fossa of the skull, and anastomoses with the iKisterior meningeal branches derived 

 from the occipital and ascending pharyngeal arteries. It gives branches to the falx cerebelli. 



