THYROID AXIS 513 



with the anterior and middle cerebral arteries through the eirele of M'illis is 

 described with the l»ranches of tlie internal carotid (page 504j. 



SUMMARY OF THE DISTRIBUTION OF THE CEREBRAL ARTERIES 



Here it may be of advantage to give a brief sunnnary of tlie distriljution of the 

 anterior, middle, and posterior cerebral arteries, the branches of wliich have already 

 been described in detail. The branches of each are divided into the central or 

 ganglionic, and the cortical or hemisi^heral. The central branches arise at the 

 commencement of the cerebral arteries about the circle of ^Mllis, whilst the cortical 

 are derived chiefly fi'om the termination of these vessels. 



(A) The central branches are divided into six sets — two median and four 

 lateral. 1. The two median are — (1) The antero-median, which arise from the 

 anterior cerebral and the anterior communicating, and sujijtly the fore end of the 

 caudate nucleus, and (2) tlie postero-median, which arise from the jjosterior 

 cerebral, and supply the inner part of the optic thalannis and neighbouring wall of 

 the third ventricle. 2. The four lateral, two on each side, are also divided into 

 antero-lateral, and postero-lateral. (1) The antero-lateral arise from the middle 

 cerebral, and, passing through the anterior perforated spot, supply the lenticular 

 nucleus, the posterior part of the caudate nucleus, the internal and external 

 capsules, and the outer part of the optic thalamus. (2) The postero-lateral arise 

 from the posterior cereljral, and supply the hinder part of the optic thalamus, the 

 crus. and the optic lobes or corpora cpiadrigemina. 



( B) Tlie cortical branches ramify in the pia mater, giving off brandies to the 

 cortical suVjstance, some ol wliich extend through it to the underlying white sub- 

 stance. The cortical branches of the anterior cerebral, roughly speaking, supply 

 the median surface of the frontal lobe as far as the precuneus, the inner part of its 

 orbital surface, and part of its convex surface, viz. the highest part of the ascend- 

 ing frontal and the first and most of the second frontal convolutions. The cortical 

 branches of the middle cerebral — or Sylvian artery as it is often called, because 

 of its relation to the Sylvian fissure — supply the most important area, namely, the 

 motor convolutions; and also the largest, namely, the inferior frontal, the ascending 

 parietal, part of tlie inferior parietal, the supramarginal and angular, the posterior 

 part of the superior parietal, the first temporal, and the anterior yjart of the second 

 and third temporal convolutions. The cortical branches of the posterior cerebral 

 supply the occipital lobe, and the inferior aspect of the temporal lobe. 



It will be seen, therefore, that the middle cerebral supplies the motor region, 

 both central and cortical, except a part of the leg centre. It also supplies the 

 region of the cortex that subserves cutaneous sensibility, the cortical auditory 

 centre, and in part the higher visual centre. It likewise supplies all the cortical 

 regions concerned in speech processes in the left hemisphere. The anterior cerebral 

 supplies only a small part of the motor region — namely, the part of the leg centre 

 that occupies the paracentral loljule and the highest part of the ascending frontal 

 convolution. The posterior cerebral supplies the visual path from the middle of 

 the tract backwards, and the half vision centre in the occipital lo)>e. It supplies 

 also the corpora quadrigemina and the sensory part of the internal capsule. 



THE THYROID AXIS 



The thyroid axis arises from the upper and front part of the subclavian artery, 

 usually opposite the internal mammary, and a little internal to the inner border of 

 the scalenus anticus. It is a short thick trunk, and divides almost immediately 

 into three radiating branches — namely, the inferior thyroid, the suprascapular, 

 and the transverse cervical ( fig. '-530 ). 



r)ccasionally the pt)sterior scajtular branch of the transverse cervical arises from 

 the third portion of the subclavian; the superficial cervical, the other branch into 

 which the transver.se cervical divides, then conimonlv comes oft' from tlie axis. 

 33 



