DEVELOPMENT OF THE HEART IN MARSUPIALS. 



495 



tlie anterior cardinal vein formed by the fusion of these two 

 vessels passes ventro-laterally to open into the Cuvierian duct. 

 This description is not, however, applicable to Peraineles. In 

 Stage V. (PI. II. fig. 7) the vena capitis medialis is continued 

 backwards into the trunk region of the embryo. The vena capitis 

 lateralis lies parallel with it and communicates with it repeatedly 

 in the anterior region ; it then diverges from it and constitutes 

 here the vessel usually known as the anterior cardinal vein, 

 opening into the Cuvierian duct. The posterior prolongation of 

 the vena capitis medialis continues as a small vessel lying alongside 



Text-figure 25. 



AC.K 



Diagram of the relations of tlie veiise capitis medialis and lateralis to the 

 primordia of the nerves. Viewed from the dorsal aspect. 



A. Stage V. Ferameles obestda (10.viii,03), B, Stage with twelve cranial nerves, 

 Perameles nasuta (13.vii.05). 



A.C.V. Anterior cardinal vein. A.V. Auditory vesicle. CD. Cuvierian duct. 

 JEL.B. Hind-brain. V.CL. Vena capitis lateralis. V.C.M. Vena capitis 

 medialis. V. Trigeminal nerve. VII. Facial nerve. JJT. & JC. Common 

 root of glosso-pharyngeal and vagus nerves. JCII. Hj'poglossal nerve. 



the neural tube in the trunk region. The Cuvierian duct arises 

 as a relatively large vessel lying in the somatopleure dorsal to 

 the posterior portion of the lateral heart- tubes. From its 

 posterior extremity there runs back a series of capillaries which 

 anastomose with capillaries arising from the prolongation of the 

 vena capitis medialis. From this line of capillaries^ which thus 



