568 



THE BLOOD-VASCULAR SYSTEM 



tributed like those to the upper spaces, akeady described, and anastomose like them with the 

 corresponding anterior branches of the lower aortic intercostals; (c) the muscular for the supply 

 of the obhque muscles of the abdomen. 



4. THE COSTO-CERVICAL TRUNK 



The costo-cervical trunk [truncus costocervicalis] (figs. 444, 463) is a short 

 stem which arises usually from the back part of the second portion of the sub- 

 clavian artery, behind the scalenus anterior on the right side, but commonly 

 just medial to that muscle on the left side. Its course is upward and backward 

 above the dome of the pleura and then downward toward the thorax, before 

 entering which it divides into its two terminal branches. 



The branches of the costo-cervical trunk are: — (1) the superior intercostal and 

 (2) the deep cervical. 



(1) The superior intercostal [a. intercostahs suprema] (fig. 463) continues the direction of 

 the costo-cervical trunk, passing downward into the thorax in front of the neck of the first rib. 

 It sometimes terminates opposite the first intercostal space by becoming the first intercostal 

 artery. Usually, however, it is prolonged downward over the neck of the second rib and suppUes 

 the second intercostal space in addition. It communicates with the highest aortic intercostal 

 artery. As it crosses the neck of the first rib the superior intercostal hes anterior (ventral) 

 to the first intercostal nerve and lateral to the superior thoracic ganglion of the sympathetic. 



Fig. 463. — Scheme of the Right Costo-cervical Trunk. (Walsham.) 



Scalenus anterior muscle 



Deep cervical branch. 



First thoracic nerve 



First intercostal nerve 

 Subclavian artery 



Second intercostal nerve 



Anterior intercostal 

 artery 

 Third intercostal'" 

 nerve 



Anterior intercostal 



artery 

 Internal mammary 

 artery 



Intercostal vessels of 

 third space 



Sympathetic nerve 



Inferior cervical 

 ganglion 



CostO"Cervical trunk 



Arteria aberrans 



Branch from first 

 aortic intercostal 



Arteria aberrans 



First aortic intercostal 

 artery 



Second aortic inter- 

 costal artery 



Intercostal vessels of fourth space 



The branches to the first and second intercostal spaces resemble in course and distribution 

 the succeeding intercostals derived from the thoracic aorta (see p. 588). Like the aortic inter- 

 costals they give off dorsal [rr. dorsales] and spinal branches [rr. spinalcs]. An arteria aberrans, 

 when present, arises from the medial side of the riglit superior intercostal, or occasionally from 

 the right subclavian itself. It descends as a slender vessel into the thorax, passing downward 

 and medially behind the oesophagus as far as the third or fourth thoracic vertebra, where in 

 some cases it anastomoses with a similar slender branch arising from the aorta below the hga- 

 mentum arteriosum. This anastomosis represents the remains of the embryonic right 

 dorsal aortic arch, and it is by its occasional enlargement that tlie anomaly of the right sub- 

 clavian artery rising from the descending portion of the aortic arch occurs (see p. 637). 



(2) The deep cervical artery (a. cervicahs profunda] passes directly backward, first between 

 the seventh and eiglith cervical nerves, and then between the transverse process of the seventh 

 cervical vertebra and the neck of tlic first rib, having the body of the seventh cervical vertebra 

 to its medial side, and the intertransverse muscle to its liitcral side. It then turns upward 

 in the groove between the transverse and spinous processes of the cervical vertebrae lying upon 

 the eemispinalis colli. It is covered by the semispinalis capitis (complexus). Between these 

 muscles it anastomoses with the deep branch of the descending branch (princeps cervicis) of 

 the occipital artery. It gives off a spinal brancli wliich enters the vertebral canal through 

 the intervertebral foramen with the eighth cervical nerve. 



.ii 



