SUPERIOR INTERCOSTAL 



519 



before the latter enters the thorax. It passes directly hac'kwartls, first between the 

 seventh and eighth cervical nerves, and then V»etween the transverse i)rocess of the 

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

 cervical vertebra to its inner side, and the intertransverse muscle to its outer side. 

 It then turns upwards in the groove between the transverse and spinous i)rocesses 

 of the cervical vertebne lying upon the semispinalis colli. It is covered by the 

 complexus. Between these muscles, near the axis, it anastomoses with the deep 

 branch of the princeps cervicis of the occipital artery. The deep cervical is homol- 

 ogous in its course to the posterior Itranch of an aortic intercostal, being morpho- 

 logically the posterior branch of tlie intercostal artery for the seventh cervical space. 

 It gives oflf the following small branches: — (a) Muscular, to the semispinalis colli 

 and complexus; (h) anastomotic, which anastomose with branches of the verte- 

 bral, ascending cervical and princeps cervicis arteries; and (/) vertebral or spinal, 



Fig. 345. — Scheme of the Right Superior Intercostal Artery. (Walsham.) 



Scalenus amicus muscle 



Deep cervical branch 



FIRST DORSAL SERl E 



FIRS T IXTERCOS T4L 

 yERVE 



Siibc/acian atlei >j 



SECOND INTERCOSTAL 

 NER VE 



Aiilerior intercostal 

 arterii 

 THIRD INTER- 

 COSTAL NERVE 



Anterior intercostal 

 artery 



Internal mammary 

 artery 



Intercostal ressels of 

 th ird space 



SYMPATHETIC 

 NER VE 



INFERIOR CERVI- 

 CAL GANGLION 



I Superior intercostal 

 J artery 



Arteria aberrans 



Branch from first aortic 

 intercostal 



Arteria aberratis 



First aortic intercostal 

 artery 



Second aortic intercostal 



artery 



Intercostal vessels ojjourth space 



which enters the spinal canal through the intervertebral foramen with the eighth 

 cervical nerve. 



(2) The first intercostal branch runs forwards in the first intercostal space, 

 and, like the second intercostal branch, which, Avhen present, runs to the second 

 space on the right side, resembles in its course and distribution the succeeding 

 intercostals derived from the aorta. (See Branches of Thoracic Aorta.) 



(3) The arteria aberrans, when jtresent, comes oft" from the inner side of the 

 right superior intercostal, and occasionally from the right subclavian itself. (See 

 jiageoOB. ) It descends as a delicate vessel into the thorax, passing liackwards 

 and inwards behind the oesophagus as far as the third or fourth thoracic vertebni, 

 where in some cases it is found to anastomose with a similar delicate branch com- 

 ing off from the aorta below the ductus arteriosus. This anastomosis, which repre- 

 sents the remains of the right dorsal aortic stem, may become enlarged, and the 

 suliclavian artery on the right side be derived from the arch of the aorta. This 

 accounts for the subclavian in such circumstances passing behind the oesophagus. 

 (See Variations of the Arch of the Aorta. ) 



