ABMORAIALITIES IX TUE CAllxXlVOUA. 



589 



The Occurrence of Two Precavcd Veins in ci Panda (text- 

 fig. 65 A). 



The innominate veins were formed as usual, but soon gave way 

 to two precaval veins (L.L). The latter at first ran posteriorly 

 and slightly mesially to points level with the anterior limit of the 

 heart, when they turned directly inwards and ran horizontally ; 

 in this part of their course each vein receives an azygos vein (M). 

 Tlie orifices of the two precaval veins and tlie wide postcaval 

 vein (T) form the angles of a triangle with the apex posterior. 



This arrangement of the precaval and postcaval veins is the 

 rule in Marsupials, but it occasionally occurs in higher Mammals. 

 The chief difference between the condition described above and 



Text-fisure 65. 



The veins of Ailurusfulff ens (A) and Meles meles (B). 

 Ex^planation of Letters. 



G. subclavian veins; H. intercostal vein; Ic. 1 and Ic. 2. intercostal veins; 

 0. esophagus : P. trachea ; Q. right recurrent laryngeal nerve ; R. internal 

 jugular vein: S. inferior thyroid vein; U. internal jugular vein ; V. vertebral 

 vein; W. externa] jugular vein. Other letters in text. 



that of the Marsupials lies in the nature of the terminal orifices. 

 In the latter the openings are closer together, and the postcaval 

 and right precaval veins are only separated by a crescentic fold. 

 In the former they are wider apart, and the crescentic fold is not 

 present. 



In the process of development the anterior cardinal veins fi-om 

 the head and the posterior cardinal veins from the body unite to 

 form the Ducts of Ouvier, which open into the sinus venosus. 

 The anterior cardinal veins become united by a transverse vessel, 

 which takes a gradually increasing share in returning the blood 

 from the left side of the head. Eventually the part of the left 

 anterior cardinal vein between this vein and the sinus venosus 



