UOLOGY 



Collateral Circulation. After ligature of the third part of the subclavian artery, the collateral 

 circulation is established mainly by three sets of vessels, thus described in a dissection : 



1. A posterior set, consisting of the transverse scapular and the descending ramus of the trans- 

 verse cervical branches of the subclavian, anastomosing with the subscapular from the axillary. 



2. A medial set, produced by the connection of the internal mammary on the one hand, with 

 the highest intercostal and lateral thoracic arteries, and the branches from the subscapular on 

 the other. 



3. A middle or axillary set, consisting of a number of small vessels derived from branches of 

 the subclavian, above, and, passing through the axilla, terminating either in the main trunk, 

 or some of the branches of the axillary below. This last set presented most conspicuously the 

 peculiar character of newly formed or, rather, dilated arteries, being excessively tortuous, and 

 forming a complete plexus. 



The chief agent in the restoration of the axillary artery below the tumor was the subscapular 

 artery, which communicated most freely with the internal mammary, transverse scapular and 

 descending ramus of the transverse cervical branches of the subclavian, from all of which it 

 received so great an influx of blood as to dilate it to three times its natural size. 1 



When a ligature is applied to the first part of the subclavian artery, the collateral circulation is 

 carried on by: (1) the anastomosis between the superior and inferior thyroids; (2) the anastomosis 

 of the two vertebrals; (3) the anastomosis of the internal mammary with the inferior epigastric 

 and the aortic intercostals; (4) the costocervical anastomosing with the aortic intercostals; (5) 

 the profunda cervicis anastomosing with the descending branch of the occipital; (6) the scapular 

 branches of the thyrocervical trunk anastomosing with the branches of the axillary, and (7) the 

 thoracic branches of the axillary anastomosing with the aortic intercostals. 



Branches. The branches of the subclavian artery are: 



Vertebral. Internal mammary. 



Thyrocervical. Costocervical. 



On the left side all four branches generally arise from the first portion of the 

 vessel; but on the right side (Fig. 520) the costocervical trunk usually springs 

 from the second portion of the vessel. On both sides of the neck, the first three 

 branches arise close together at the medial border of the Scalenus anterior; in 

 the majority of cases, a free interval of from 1.25 to 2.5 cm. exists between the 

 commencement of the artery and the origin of the nearest branch. 



1. The vertebral artery (a. vertebralis) (Fig. 514), is the first branch of the sub- 

 clavian, and arises from the upper and back part of the first portion of the vessel. 

 It is surrounded by a plexus of nerve fibers derived from the inferior cervical 

 ganglion of the sympathetic trunk, and ascends through the foramina in the 

 transverse processes of the upper six cervical vertebrae; 2 it then winds behind the 

 superior articular process of the atlas and, entering the skull through the foramen 

 magnum, unites, at the lower border of the pons, with the vessel of the opposite 

 side to form the basilar artery. 



Relations. The vertebral artery may be divided into four parts: The first part runs upward 

 and backward between the Longus colli and the Scalenus anterior. In front of it are the internal 

 jugular and vertebral veins, and it is crossed by the inferior thyroid artery; the left vertebral 

 is crossed by the thoracic duct also. Behind it are the transverse process of the seventh cervical 

 vertebra, the sympathetic trunk and its inferior cervical ganglion. The second part runs upward 

 through the foramina in the transverse processes of the upper six cervical vertebra?, and is sur- 

 rounded by branches from the inferior cervical sympathetic ganglion and by a plexus of veins 

 which unite to form the vertebral vein at the lower part of the neck. It is situated in front of 

 the trunks of the cervical nerves, and pursues an almost vertical course as far as the transverse 

 process of the atlas, above which it runs upward and lateralward to the foramen in the trans- 

 verse process of the atlas. The third part issues from the latter foramen on the medial side of 

 the Rectus capitis lateralis, and curves backward behind the superior articular process of the 

 atlas, the anterior ramus of the first cervical nerve being on its medial side; it then lies in the 

 groove on the upper surface of the posterior arch of the atlas, and enters the vertebral canal 

 by passing beneath the posterior atlantooccipital membrane. This part of the artery is covered 

 by the Semispinalis capitis and is contained in the suboccipital triangle a triangular space 





