56 ANATOMY OF THE RAT 



vein, giving off branches to the internal intercostal muscles. 

 Trace it posteriorly along the dorsal surface of the rectus 

 abdominis muscle, to which it sends branches. Several 

 branches perforate the intercostal muscles and supply the 

 pectoral and rectus abdominis muscles. Find the right 

 internal mammary artery. Its branches and course are 

 substantially the same as for the left internal mammary. 



The vertebral artery upon leaving the subclavian passes 

 cephalad about half a centimeter and enters the verte- 

 hrarterial canal at the sixth cervical vertebra. This canal 

 consists of the transverse foramina of the cervical vertebrae. 

 Running forward through this canal, the artery sends off 

 branches between the vertebrae. It traverses the transverse 

 foramen of the atlas, gives off a branch through the large 

 oval foramen on the dorsal side of this vertebra, passes 

 through the atlantal foramen, and enters the cranial cavity 

 by way of the foramen magnum. 



Thyro-cervical trunk. It leaves the subclavian artery 

 medial to the first rib and passes anterolaterally to a position 

 dorsal to the proximal end of the clavicle, where it divides 

 into several branches. These branches supply glands on the 

 surface of the neck, and muscles of the neck region. 



Costo-cervical trunk. This vessel leaves the subclavian 

 artery at the same level as the internal mammary, courses 

 laterally anterior to the first rib, then sends branches to the 

 lateral muscles of the thorax and deeper muscles of the neck. 



The axillary artery is the continuation of the subclavian 

 lateral to the first rib. Its branches are as follows. 



(1) Lateral thoracic artery. It proceeds caudally from 

 the axillary artery along the medial surface of the cutane- 

 ous maximus muscle. 



(2) Suhscapiilar artery. It arises from the axillary ar- 

 tery and divides into branches which supply muscles in 

 the upper arm and thorax. 



