THYROID AXIS BRANCHES. 285 



larger than the rest, passes along the crus cerebelli to be distributed 

 to the anterior border of the cerebellum. This may be called the 

 middle cerebellar artery. 



The Superior cerebellar arteries, two of the terminal branches of 

 the basilar, wind around the crus cerebri on each side in relation 

 with- the fourth nerve, and are distributed to the upper surface of 

 the cerebellum inosculating with the inferior cerebellar. This 

 artery gives off a small branch which accompanies the seventh 

 pair of nerves into the meatus auditorius internus. 



The Posterior cerebral arteries, the other two terminal branches 

 of the basilar, wind around the crus cerebri at each side, and are 

 distributed to the posterior lobes of the cerebrum. They are sepa- 

 rated from the superior cerebellar artery, near the origin, by the 

 third pair of nerves, and are in close relation with the fourth pair 

 in their course around the crura cerebri. Anteriorly, near their 

 origin, they give off a tuft of small vessels, which enter the locus 

 perforatus, and they receive the posterior communicating arteries 

 from the internal carotid. They also send a branch to the velum 

 interpositum and plexus choroides. 



The communications established between the anterior cerebral 

 arteries in front, and the internal carotids and posterior cerebral 

 arteries behind, by the communicating arteries, constitute the circle 

 of Willis. This remarkable communication at the base of the 

 brain is formed by the anterior communicating branch, anterior 

 cerebrals, and internal carotid arteries in front, and by the posterior 

 communicating, posterior cerebrals, and basilar artery behind. 



The THYROID Axis is a short trunk which divides almost imme- 

 diately after its origin into four branches, some of which are occa- 

 sionally branches of the subclavian artery itself. 



The INFERIOR THYROID ARTERY ascends obliquely in a serpentine 

 course behind the sheath of the carotid vessels, to the inferior part 

 of the thyroid gland, to which it is distributed, and sends branches 

 to the trachea, lower part of the larynx, and oesophagus. It is in 

 relation with the middle cervical ganglion of the sympathetic, 

 which lies in front of it. 



The SUPRA-SCAPULAR ARTERY (transversalis humeri) passes ob- 

 liquely outwards behind the clavicle, and over the ligament of the 

 supra-scapular notch, to the supra-spinatus fossa. It crosses in its 

 course the scalenus anticus muscle, phrenic nerve and subclavian 

 artery, is distributed to the muscles on the dorsum of the scapula, 

 and inosculates with the posterior scapular, and beneath the acro- 

 mion process with the dorsal branch of the subscapular artery. 

 At the supra-scapular notch it sends a large branch to the trape- 

 zius muscle. The supra-scapular artery is not unfrequently a 

 branch of the subclavian. 



The POSTERIOR SCAPULAR ARTERY (transversalis colli) passes 

 transversely across the subclavian triangle at the root of the neck, 

 to the superior angle of the scapula. It then descends along the 

 posterior border of that bone to its inferior angle, where it inoscu- 



