ii2 THORAX 



crossing posterior to the aorta and the thoracic duct, it joins 

 the vena azygos. Before it terminates it may receive the 

 accessory hemiazygos vein. 



The thoracic tributaries of this vein are the intercostal 

 veins of the lower three spaces of the left side and the left 

 subcostal vein. In the abdomen it receives the upper two 

 left lumbar veins. 



The Anterior Intercostal Veins. The blood is drained 

 from the anterior part of the thoracic wall by veins which 

 accompany the intercostal branches of the internal mammary 

 arteries. They terminate in the internal mammary veins. 



The veins of the thoracic parietes are extremely variable, and the 

 description given above must be looked upon as representing merely their 

 more usual arrangement. 



THORACIC JOINTS. 



The dissector should now complete the dissection of the 

 thorax by an examination of the various thoracic joints. 



Dissection. When the portion of the sternum with the cartilages of the 

 ribs, which was laid aside, is studied, the following joints will be noted : 

 inter-sternal, costo-sternal, and inter-chondral. Very little dissection is 

 necessary. After the ligaments have been defined, the dissector should 

 remove a thin slice from the anterior aspect of each articulation, in order 

 that the interior of the joint may be displayed. 



Synchondrosis Sternalis. The joint between the manu- 

 brium and the body of the sternum is a synchondrosis. The 

 opposing surfaces of bone are covered with a layer of hyaline 

 cartilage, and are united by intermediate fibre-cartilage. The 

 joint is supported by some anterior and posterior longitudinal 

 fibres which are developed in connection with the strong and 

 thick periosteum. The posterior ligament is the stronger of 

 the two. The joint between the body of the sternum and the 

 xiphoid process is also a synchondrosis till middle life, at 

 which period the two parts become ossified together. 



Sterno-chondral Articulations. Seven ribs articulate with 

 each side of the sternum by means of their cartilages. 



The articulations of the first and the sixth are peculiar, inasmuch as 

 they articulate with single pieces of the sternum, viz. with the manubrium 

 and the lowest piece of the body, respectively ; whereas each of the cartilages 

 of the other true ribs articulates with two segments of the sternum. The 

 cartilage of the first rib is implanted upon the side of the manubrium 



