PLATE IV 



Plate IV is from a section through the upper half of the 

 first thoracic vertebra posteriorly, the middle of the clavicles 

 anteriorly and the middle of the glenoid cavities of the 

 scapulae laterally. The plane of the section is 1.3 cm. pos- 

 teriorly and 1.1 cm. anteriorly below that of section III so 

 that the anterior margin is 2.6 cm. below the posterior. 



The thoracic duct is cut through the uppermost part of 

 the arch. The internal part is the ascending limb, the ex- 

 ternal the descending limb. A valve is present at the junc- 

 tion of the two limbs. 



So 



