SUBCLAVIAN ARTERIES. 



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and the mammary gland. In both these latter 

 situations the arteries in question communi- 

 cate freely with the external thoracic branches 

 of the axillary, thus forming an important 

 connection between the circulation of the in- 

 terior and that of the exterior of the thorax. 



The terminal branches of the internal mam- 

 mary artery are two in number, viz. internal 

 terminal branch (Ranms abdominalis) and an 

 external (Arteria muscufo-phrenica, Haller). 



4. The internal, or the abdominal branch, 

 is the smaller of the two, yet in direction it 

 represents the parent trunk. Having communi- 

 cated with the artery of the opposite side be- 

 hind the xiphoid cartilage, it escapes from the 

 thorax through a small triangular interval 

 between the fibres of the diaphragm, and 

 then immediately enters the sheath of the 

 rectus abdominis, descending between the 

 muscle and the posterior lamina of the sheath. 

 Having arrived opposite the umbilicus, it be- 

 comes distinctly continuous with ascending 

 branches of the internal epigastric artery ; it 

 likewise furnishes many branches to the sub- 

 stance of the rectus muscle, and others which, 

 piercing the sheath, are widely distributed to 

 the broad muscles of the abdomen. 



5. The external terminating branch (or the 

 arteria musculo-phrenica), is larger than the 

 internal, from which it separates nearly at 

 right angles, passing almost transversely out- 

 wards in a curved course along the superior 

 line of attachment of the diaphragm to the 

 false ribs. In this course the artery gives off, 

 a. numerous phrenic branches of large size, 

 which enters the diaphragm all along its cos- 

 tal attachment ; and b. anterior intercostal 

 branches^ which supply the lower intercostal 

 spaces in precisely the same manner as those 

 from the mammary trunk supply the upper, 

 and which have been already described. 



Varieties. The mammary artery presents 

 but few varieties either of origin or position ; 

 in 290 out of 297 examinations, this artery 

 occupied its normal position. In one in- 

 stance it arose beneath, in six instances ex- 

 ternal to the scalenus muscle, and in one only 

 of the six was it derived from the axillary 

 artery (Quain). 



Much more rarely still does the mammary 

 artery deviate in the opposite direction, i.e. 

 inwards ; it has, however, been seen to spring 

 from the arch of the aorta, and also from the 

 arteria innominata. Occasionally too it arises 

 in common with the thyroid axis. 



Two veins (one on either side of it) accom- 

 pany each internal mammary artery ; they are 

 formed by branches corresponding to those 

 given oft' by the artery, with the exception 

 (according to Cruveilhier) of the vein accom- 

 panying the arteria comes nervi phrenici, 

 which on both sides terminates separately. 

 On the right side the mammary veins open into 

 the commencement of the vena cava; on the 

 left side, they are connected with the corre- 

 sponding vena innominata. " The mammary 

 arteries are remarkable for the number of 

 their inosculations, and for the distant parts 

 of the arterial system which they serve to 



connect : they anastomose with each other, 

 and their inosculations with the thoracic aorta 

 encircle the thorax. On the parieties of this 

 cavity their branches connect the axillary 

 and subclavian arteries ; on the diaphragm 

 they form a link in the chain of inosculations 

 between the subclavian artery and abdominal 

 aorta ; and in the parieties of the abdomen 

 they form an anastomosis most remarkable for 

 the distance between those vessels which it 

 serves to connect, namely, the arteries of the 

 superior and inferior extremities."* 



III. Thyroid a.vis. This artery springs 

 from the anterior aspect of the subclavian 

 trunk, close to the inner edge of the scalenus 

 anticus muscle, and consequently from the 

 very last portion of the artery in its first 

 stage. 



The thyroid axis forms a trunk only a few 

 lines in length, which projects forwards and a 

 little upwards : the phrenic nerve is applied 

 against the outer surface of this artery, and 

 still retains the same relation to it, even where 

 the artery arises more externally than usual, 

 as if in such cases the nerve were drawn 

 outwards by the artery. This arrangement 

 was observed where the thyroid axis arose 

 from the third stage of the subclavian. The 

 thyroid axis usually terminates in three 

 branches : 



1. Inferior thyroid artery. From the thy- 

 roid axis, this branch passes a little upwards, 

 and then turns inwards and backwards, de- 

 scribing a curve, of which the concavity looks 

 forwards and downwards, corresponding to 

 the carotid sheath. The artery next descends, 

 but soon afterwards inclines upwards and in- 

 wards until it reaches the thyroid body, thus 

 forming a second curve the reverse of the 

 former one, for the concavity of this second 

 curve looks upwards and backwards, and is 

 crossed anteriorly by the recurrent nerve. 



The anterior relations of this artery are the 

 following : 



It is crossed in its first curve, opposite the 

 sixth cervical vertebra, by the sympathetic 

 nerve, which more frequently on the right 

 than on the left side however, joins the middle 

 cervical ganglion in this situation. The inter- 

 nal jugular vein, vagus nerve, and carotid 

 artery, contained in their common sheath, are 

 the next parts which cross the artery ; and 

 lastly, the recurrent nerve, sub-hyoid muscles, 

 and thyroid gland, lie in front of it. 



The recurrent nerve lies in front of the 

 second curve of the artery. 



The inferior thyroid artery is posteriorly 

 in relation with the vertebral artery, the longus 

 colli muscle, and the vertebral column ; and, 

 on the left side, with the oesophagus and tho- 

 racic duct. 



The thoracic duct very frequently passes 

 up behind the inferior thyroid artery to the 

 level of the sixth cervical vertebra, where, 

 bending downwards and forwards, it arches 

 over that vessel and descends in front of it, 

 to terminate in the subclavian vein. 



* Harrison's Surgical Anatomv of the Arteries. 

 4th Edition, p. 141. Dublin. 



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