408 DISSECTION OF THE PIGEON 



4. The structure of the lungs. 



Pass a seeker along one of the bronchi, and sUt it open 

 with scissors. Follow the branches of the bronchus through 

 the lungs, and note the openings of the various air-sacs de- 

 scribed above {p. 390). 



VII. DISSECTION OP THE EXOBETOEY AND EEPEO- 

 DUCTIVE SYSTEMS. 



These may conveniently be considered together, because, as 

 in the rabbit, the genital ducts are in both sexes formed from 

 what were originally parts of the excretory system. 



In the male the vas deferens is formed from the meso- 

 nephric duct : in the female the oviduct is formed from the 

 pronephric duct. In both sexes the kidneys and ureters of 

 the adult are formed from the hindmost division of the kidneys 

 of the embryo, i.e. the metanephra, and the metanephric ducts. 



A. The Male Pigeon. 

 1. The urinary system. 



a. The kidneys are a pair of solid three-lobed bodies, 



firmly imbedded in the ventral wall of the pelvis, 

 and lying immediately behind the lungs. Their 

 ventral surfaces are covered by peritoneum. 



b. The ureters are a pair of straight narrow tubes. 



Each arises in the substance of the anterior lobe 

 of its kidney, emerges between the anterior and 

 middle lobes, and runs backwards along the inner 

 side and ventral surface of the middle and posterior 

 lobes, and then straight back to the dorsal wall of 

 the cloaca. 



Slit up one of the ureters, and follow it into the anterior 

 lobe of the kidney, noting the openings of smaller ducts into 

 it at intervals along its length. 



c. The adrenals are a pair of small, elongated, yellowish 



bodies, attached to the ventral surface of the 



