THE BRANCHES OF THE ARCH OF THE AORTA 261 



(a) Several tranxrerse arteries on each side. One, the auditory, 

 enters the internal meatus; another, the anteroinferior cercbellar, 

 to the anterior border of the cerebellum. 



(6) The superior cerebellar, to the upper surface, joining the 

 inferior cerebellar. 



(c) The posterior cerebrals, to the under surface of the posterior 

 lobes, receiving the posterior co7nrn.unica.ting. They give off the 

 posterior choroid branches and supply the posterior perforated 

 space. 



The circle of Willis is situated at the base of the brain, it is 

 an anastomosis formed by the bloodvessels of the brain. The 

 arteries entering into its formation are : In front, the two anterior 

 cerebral arteries, branches of the internal carotid, which are 

 connected by the anterior communicating artery; behind, by 

 two posterior cerebral arteries, branches of the basilar, and these 

 communicate laterally with the internal carotids through the 

 posterior communicating arteries. The parts of the brain 

 included within this arterial circle are: The lamina terminals, 

 the chiasm of the optic nerves, tuber cinereum, corpora albi- 

 cantia, and the posterior perforated substance. 



II. The thyroid axis arises from the forepart of the subclavian, 

 and divides close to its origin into the inferior thyroid, supra- 

 scapular, and transverse cervical. 



1. The inferior thyroid, to the gland behind the sympathetic 

 and the common carotid, joins its fellow and the superior thyroid, 

 giving off the following branches: 



(a) Inferior laryngeal, runs with the recurrent nerve; (6) 

 tracheal, joining the bronchial arteries; (c) esophageal; (d) to 

 the inferior constrictor and hyoid depressor muscles and the 

 scaleni; and (c) the ascending cervical. 



The last named runs between the scalenus anticus and the 

 rectus anticus major, joining the vertebral and giving other 

 branches which, with the lateral spinal of the vertebral, help 

 form the anterior median artery of the cord. 



2. The suprascapular runs at first between the scalenus anticus 

 and the sternomastoid, crosses the subclavian, and runs behind 

 the clavicle to cross the transverse ligament of the scapula. 

 In the supraspinous fossa it runs beneath the muscle, which it 

 supplies, and crossing the neck of the scapula terminates in the 

 infraspinatus, where it joins the dorsal and posterior scapular 

 artery. A supraacromial branch joins the acromiothoracic 



