646 THE ARTERIES. 



muscles. Frequently, the second intercostal and its spinal branch come directly 

 from the doi*sal artery ; the fifth also often arises from the posterior aorta.^ 



On the right side, the dorsal artery always proceeds from a trunk common to 

 it and the superior cervical artery — a circumstance sometimes observed in the 

 left. This trunk has no relation with the oesophagus. 



2. Superior Cervical, Cervico-muscular, or Deep Cervical Artery 

 (Fig. 375, 6). 



This vessel arises in front of the preceding artery, has the same relations in 

 the thoracic cavity, which it leaves by passing between the two first ribs, behind 

 the last costo-transverse articulation ; ^ it is then directed upwards and forwards, 

 passing beneath the inferior branch of the longissimus dorsi and complexus 

 muscles, courses in a flexuous manner through the space comprised between the 

 latter muscle on one side, and the superior branch of the longissimus dorsi and 

 cervical ligament on the other, and aiTives at the second vertebra of the neck, 

 where its terminal divisions anastomose with the branches of the occipito- 

 muscular, vertebral, and even the dorsal arteries. 



The superior cervical artery distributes in its course : 1. The first intercostal 

 arteiy and the first spinal branch. 2. Very numerous branches which are 

 expended in the muscles and integuments of the cervical region, as well as in the 

 large hgament occupying the middle plane of that region ; among these branches, 

 one longer than the others traverses the complexus muscle to place itself between 

 it and the splenius, and is sometimes supplemented in great part by the dorsal 

 artery. 



3. Vertebral Artery (Fig. 375, 7). 



Arising at an acute angle from the axillary artery at the first intercostal space, 

 and covered at its origin by the mediastinal layer, the vertebral artery proceeds 

 forward and upward, within the first rib, outside the oesophagus,^ the trachea, 

 and the inferior cervical ganglion, and is situated at the bottom of the interstice 

 separating the two portions of the scalenus, with the fasciculus of branches 

 arising from the brachial plexus, which is a little above the vessel. It then 

 passes beneath the transverse process of the seventh cervical vertebra, and 

 traverses the series of cervical foramina, hidden beneath the iutertransversahs 

 colli, to anastomose in full canal with the retrograde branch of the occipital 

 artery, at the atlo-axoid articulation, underneath the obliquus capitis posticus 

 muscle. 



In its track, it detaches at each intervertebral space numerous branches, 

 which may be divided into inferior, superior, external, and internal. The first 

 chiefly pass to the scalenus, longus colli, and rectus capitis anticus major. The 

 second, which are incomparably larger and more numerous than all the others, 

 are destined to the complexus and trachelo-mastoideus, semispiualis, and longis- 

 simus dorsi muscles ; they anastomose with the divisions of the superior cervical 

 and occipito-muscular arteries. The external branches are very small, and pass 

 to the intertransversalis muscle. The internal branches enter the intervertebral 

 foramina to join the middle spinal artery. 



' For the description of these arteries, see p. 611. 



» We liave seen it escape, along with the dorsal artery, by the second intercostal space. 



* On the right, these relations with the oesophagus are not present. 



