THE nilAClHAL on AXII.I.M;} .1 /,//:/,' 



full canal with the retrograde branch of the occipital artery, at tho atlo-axoid 

 articulation. underneath the great oblique muscle of the head. 



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

 which may !>. divided into inferior, superior, external, and internal. The 

 first chiefly pass to the scalemis, longus colli, and tho great anterior rcctus 

 muscle of the head. The second, which are incomparably larger and more 

 numerous than all the others, are destined to tho two complex muscles, the 

 transverse-spinous (scmispinalis) muscles of the neck, and to the ilio-spinal 

 muscle ; they anastomose with tho divisions of the superior cervical and 

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

 to tho intertransverse muscles. The internal branches enter the inter- 

 vertcbral foramina to join tho middle spinal artery. 



4. Internal Thoracic, or Internal Mammary Artery. (Fig. 282, 9.) 



The internal thoracic artery emerges from the brachial trunk at the 

 first rib, and immediately descends along tho inner face of that bone to the 

 sternum, remaining covered by the pleura. It then bends backwards, passes 

 under the triangular muscle and above the sternal cartilages, which it 

 crosses near the ehondro-sternal articulation, and reaches the base of tho 

 xiphoid appendix, where it ends in two branches : one abdominal, the other 

 tlmrarii-, and which have been named the anterior abdontinal and asternal 

 art i ries. 



In its course, the internal thoracic artery sends off collateral branches 



which may bo distinguished into superior, inferior, and external. The 



are always very slender, and proceed to the pericardium and 



mediastinum. The inferior (Fig. 282, 11) are very large, and traverse the 



intercostal spaces to enter the pectoral muscles, where they meet the ramifi- 



s of the external thoracic artery. The external branches (Fig. 282, 10) 



follow the intercostal spaces; each generally divides into two branches, 



which finally anastomose by inosculation with the terminal divisions of the 



first seven intercostal arteries. 



'.ml ///-'////-A. -x of (In internal tJtoracic artery. 1. Anterior ab- 



il ;/(,;/. This vessel separates from tho asternal artery at an acute 



angle, and passes directly backward to escape from the chest by c.>ur.-.ing 



ith tin: xiphoid appendix; it then places itself on the superior l'< 

 tlie rectus muscle of the abdomen, which it enters, after detaching literal 

 1. ranches to the alidominal walls, and anastomoses by its terminal ramifica- 

 tions with the posterior abdominal artery. 



2. Asternal tirti-rif. This vessel glides within the cartilaginous circle 



formed by the false ribs, in crossing the digitations of the transverse nm-elc 



of the abdomen, and terminates at the thirteenth intercostal space, in which 



it ascends to anastomose with tho corresponding intercostal artery. It 



supplies in its track: intercostal branches, which comjM>rt themselves like 



.1 1 alogons branches of the internal thoracic artery; fine diaphragmatic 



; and abdominal divisions, which particularly ramify in the tranvorso 



muscle. 



5. EjL-li-nial or Inferior Thoracic, or Kj-h-nml Munwnry Aft fry. 



(Fig. 282, I'J. i 



Principally de.-tin- d to tin- deep pectoral muscles, this artery conn. 

 at an a -iite angle in front of, but close to, the preceding, turns tin- ant 



the first rib, and then passes back against the inten. : the 



pectoral and stcrno-prcscapular muscles, in which are expended its 



2 o 2 



