BBAXCHES OF THE SUBCLAVIAX ARTERY. 583 



cord and to the eauda equina. Branches from these vessels form a free anasto- 

 mosis round the posterior roots of the spinal nerves, and communicate, by means 

 of very tortuous transverse branches, with the vessel of the opposite side. At its 

 commencement it gives off an ascending branch, which terminates on the side of 

 the fourth ventricle. 



The posterior inferior cerebellar artery (Fig. 354). the largest branch of the 

 vertebral, winds backward round the upper part of the medulla oblongata, passing 

 between the origin of the pneurnogastric and spinal accessory nerves, over the 

 restiform body to the under surface of the cerebellum, where it divides into two 

 branches an internal one. which is continued backward to the notch between 

 the two hemispheres of the cerebellum ; and an external one. which supplies the 

 under surface of the cerebellum as far as its outer border, where it anastomoses 

 with the anterior inferior cerebellar and the superior cerebellar branches of the 

 basilar artery. Branches from this artery supply the choroid plexus of the fourth 

 ventricle. 



Surgical Anatomy. The vertebral artery has been tied in several instances: 1. tor 

 wounds or traumatic aneurism : '2. after ligature of the innominate, either at the same time to 

 prevent haemorrhage, or later on to arrest bleeding where it has occurred at the seat of ligature ; 

 and 3. in epilepsy. In these latter cases the treatment has been recommended by Dr. 

 Alexander of Liverpool, in the hope that by diminishing the supply of blood to the posterior 

 part of the brain and the spinal cord a diminution or cessation of the epileptic fits would result 

 The operation of ligature of the vertebral is performed by making an incision along the posterior 

 border of the Sterno-mastoid muscle, just above the clavicle. The muscle is pulled to the 

 inner side, and the anterior tubercle of the transverse process of the sixth cervical vertebra 

 sought for. A deep layer of fascia bejng now divided, the interval between the Scalenus anticus 

 and the Longus colli just below their insertion into the tubercle is defined, and the artery and 

 vein found in the interspace. The vein is to be drawn to the outer side, and the aneurism 

 needle passed from without inward. Drs. Raniskill and Bright have pointed out that severe 

 pain at the back of the head may be symptomatic of disease of the vertebral artery just 

 before it enters the skull. This is explained by the close connection of the artery with the sub- 

 occipital nerve in the groove on the posterior arch of the atlas. Disease of the same artery has 

 been also said to affect speech, from pressure on the hypoglossal where it is in relation with 

 the vessel, leading to paralysis of the muscles of the tongue. 



The Basilar Artery, so named from its position at the base of the skull, is 

 a single trunk formed by the junction of the two vertebral arteries ; it extends 

 from the posterior to the anterior border of the pons Varolii, lying in its 

 median groove, under cover of the arachnoid. It ends by dividing into two 

 branches, the posterior cerebral arteries. Its branches are, on each side, the 

 following : 



Transverse. Superior Cerebellar. 



Anterior Inferior Cerebellar. Posterior Cerebral. 



The transverse branches supply the pons Varolii and adjacent parts of the 

 brain, one branch, the internal auditory, accompanies the auditory nerve into 

 the internal auditory ineatus : and another, the anterior inferior cerebellar artery, 

 passes across the crus cerebelli, to be distributed to the anterior border of the 

 under surface of the cerebellum. 



The superior cerebellar arteries arise near the termination of the basilar. 

 They wind round the crus cerebri close to the fourth nerve, and, arriving at the 

 upper surface of the cerebellum, divide into branches which ramify in the pia 

 mater and anastomose with the branches of the inferior cerebellar artery. Sev- 

 eral branches are given to the pineal gland and also to the velum interpositum. 



The posterior cerebral arteries, the two terminal branches of the basilar, are 

 larger than the preceding, from which they are separated near their origin by the 

 third nerves. Winding round the cms cerebri, they pass to the under surface of 

 the occipital lobes of the cerebrum and divide into three main branches. Xear 

 their origin they receive the posterior communicating arteries from the internal 

 carotid. The branches of the posterior cerebral artery are 



Postero-median Ganglionic. Postero-lateral Ganglionic. 



Posterior Choroid. Three Terminal. 



