118 ILLINOIS STATE ACADEMY OF SCIENCE 



111 contrast to the fused relations of the arterial sys- 

 tems, the venous systems were found to be completely 

 independent of each other. Post cavae are normally pre- 

 sent, and these are joined in each liver by respective um- 

 bilical veins, from whence a single vessel continues for- 

 ward into the right auricle of the respective heart. These 

 are joined by precavae coming from adjacent regions, 

 although the two anterior vena cavae are independent of 

 each other. 



Within the hearts, normal relations were found to exist. 

 Completely four-chambered structures were developed 

 and normal canals and valves separated the chambers 

 from each other. Well-defined Botall's ducts were iden- 

 tified between the pulmonaries and the adjacent aortic 

 arches. 



THE RESPIRATORY SYSTEM 



Two complete sets of lungs are developed, and these 

 lie in independent pleural cavities, separated by double 

 folds of visceral pleurae. These cavities lie around the 

 heart, and each pair of lungs is connected to its respec- 

 tive heart by normal pulmonary arteries and veins. The 

 ventral lungs, characteristically lobulated, are slightly 

 larger than the more dorsal pair and are understood to 

 belong to the larger pig as evidenced by the vascular 

 connections. Normal bronchioles and bronchi with nor- 

 mal cartilage supports are developed, and from the junc- 

 tion of the two bronchi, normal tracheae extend forward 

 to the neck into the pharynx. As indicated above, these 

 tracheae lie one above and the other below the unpaired 

 oesophagus. 



Anteriorly, each trachea continues into a larynx, ap- 

 parently normal, with the three characteristic cartilages 

 present, but somewhat distorted and partially fused. A 

 greatly modified basihyal cartilage is present, and this is 

 continuous with the hyoid apparatus, consisting of four 

 parts. The hyoids, which are continuous with the ventral 

 larynx, are more nearly normal, and the distal tympano- 

 hyals join the auditory bulla of each temporal bone. On 

 the other hand, the hyoids of the more dorsal larynx are 

 greatly reduced, because of the cramped position; but 

 each continues upward through the connective tissue re- 



