522 THE BLOOD-VASCULAR SYSTEM. 



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. 



The bulbar arteries comprise several minute vessels which spring from the 

 vertebral and its branches and are distributed to the medulla oblongata. 



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

 wounds or traumatic aneurism ; 2, after ligation of the innominate, either at the same time to 

 prevent hemorrhage, 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, 

 But, on account of the uncertainty as to what cases, if any, derived benefit from the operation, 

 it has now been abandoned. The operation of ligation 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 being now divided, the interval be- 

 tween the Scalenus anticus and the Longus colli just below their attachment to 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. Eamskill 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 connec- 

 tion of the artery with the suboccipital 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 hypo- 

 glossal where it is in relation with the vessel, leading to paralysis of the muscles of the 

 tongue. 



The Basilar Artery (Fig. 291), 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 ex- 

 tends 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 the two 

 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 in- 

 ternal auditory meatus. 



The anterior inferior cerebellar artery passes backward across the crus cerebelli, 

 to be distributed to the anterior border of the under surface of the cerebellum, 

 anastomosing with the posterior inferior cerebellar branch of the vertebral. 



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

 pass outward, immediately behind the third nerves, which separate them from the 

 posterior cerebral, wind round the crura 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, reaching the circumference of the cerebellum, anastomose 

 with the branches of the inferior cerebellar arteries. Several branches are given 

 to the pineal gland, the valve of Vieussens, and 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. Passing outward, parallel to the superior cerebellar artery, and 

 receiving the posterior communicating from the internal carotid, they wind round 

 the crura cerebri, arid pass to the under surface of the occipital lobes of the cere- 

 brum, and break up into branches for the supply of the temporal and occipital 

 lobes. The branches of the posterior cerebral artery are : 



Postero-median ganglionic. ( Anterior temporal. 



Posterior choroid. Three terminal. < Posterior temporal. 



Postero-lateral ganglionic. ( Occipital. 



