4T8 Anatomy and Development of Veins of Chelonia 



small anastomosing branch. As has already been stated, they open into 

 the portal veins of the liver. 



The posteava arises by two short branches between the kidneys and 

 extends forward as an unpaired vessel ventrolateral to the aorta and, 

 after passing through the liver, opens into the right side of the sinus 

 venosus. The two root branches receive the renal, suprarenal, and sper- 

 matic revehent veins. The unpaired portion receives only the revehent 

 veins of the liver. 



The Chelonia differ from both the Lacertilia and the Ophidia in the 

 possession of an unpaired posteava. 



DEVELOPMENT OF THE REXAL PORTAL SYSTEM. 



Development of the posteava. — The veins to be considered in this con- 

 nection are the postcardinals and the subcardinals. Owing to the fact 

 that these veins are already laid down in the 7.4 mm. embryo, it will not 

 be possible to trace their earliest development in this reptile. According 

 to Eabl, 92, and Hoffmann, 93, who investigated the earlier development 

 of the postcardinals in the selachians, these veins arise by a longitudinal 

 fusion of the intersegmental branches of the aorta. Brouha, 98, in his 

 investigations on the development of the liver in birds, finds that in a 

 chick embryo of 47 hrs., the postcardinals and umbilicals are not yet 

 formed. There is found, however, in the body-walls caudad of the 

 sinus venosus a network of vessels wdiich open into the ducts of Cuvier. 

 In a 62 hr. chick embryo, two vessels, which are still connected by a 

 number of cross branches, are formed from this network. The outer of 

 these vessels is the postcardinal, while the inner represents the umbilical. 

 It is not until the 72 hr. stage is reached that these cross branches com- 

 pletely disappear. Lewis, 04, finds that in the rabbit the postcardinal 

 veins appear later than the umbilicals. " The umbilical vein sends 

 branches toward the aorta, into the posterior limb and less distinctly into 

 the anterior limb. A longitudinal anastomosis of these vessels, uniting 

 with a sprout from the venous end of the heart, produces the posterior 

 cardinal vein, which then is cut off from the umbilical vein, carrying 

 with it the veins from the limbs." (Lewis: Am. Jour. Anat., Vol. Ill, 

 p. XII.) 



In a turtle embryo of 7.4 mm. the postcardinal veins extend forward 

 from the caudal termination of the mesonephric ducts along the entire 

 length of the mesonephroi, dorsolateral to the mesonephric ducts. Xo 

 distinct caudal vein is yet formed. At the caudal termination of the 

 mesonephric ducts the postcardinal of each side receives a number of 

 small branches from the tail, the last dorsal intersegmental branch, and 



