DEVELOPMENT OF THE HEART IN MARSUPIALS. 



499 



EXPLANATION OP THE PLATES. 



Lettei'iny . 



A. Auricle. 

 A.\, A. 2, A. 3. First, second and tliird 

 aortic arches. 

 A.C. Aiigioblast celL 

 A.C.V. Anterior cardinal vein. 

 A. I. P. Anterior intestinal portal. 

 A.JSf. Auditory neuroniere. 

 A.V. Auditory vesicle. 

 A.V.C. Auriculo-ventricular con- 

 striction. 

 S.A. Bulbus arteriosus. 

 CD. Cuvierian duct. 

 D.A. Dorsal aorta. 

 JEtid. Endothelium of heart. 

 F.G. Fore-gut. 



G. Gut. 

 S.S. Hind-brain. 

 I.e. Internal carotid artery. 

 M.M.F. Margin of the medullary 

 plate. 

 III/. Mj'ocardium. 

 F. Pericardium. 

 P.p.C. Pleuro-i)ericardial canal. 

 T. G. Trigeminal ganglion. 

 V. Ventricle. 

 V.C.L. Vena capitis lateralis. 

 V.C.M. Vena capitis medialis. 

 V.P.I. ,J".P.2. First and second visceral 

 pouches. 



Pjlate I. 



Figures 1-5 represent graphic reconstructions of the anterior ends of five embryos, 

 viewed from the ventral aspect and all drawn at the same magnification. 



The outline of the gut is indicated b3' a broken line and its area is stippled, 

 except where it is covered by the pericardium. The limits of the peri- 

 cardium are indicated by a fine black line and its area is coloured grey. 

 The endothelial heart-tubes, the aorta and the aortic arches are coloured 

 red. The outline of the brain-plate is shown as a heavj' black line where- 

 ever it was possible to determine its limits. In the region of the neural- 

 crest proliferation in Stage I., the margin of the meduUai'y plate is 

 indistinct ; a dotted line here indicates its probable outline. 



The outlines of the gut, pericardium, and brain-plate were plotted on one 

 side only, and the second side is a duplicate of the first, except in the case 

 of figure 1 {Perameles obesula 1 Z), where the pericardium was plotted on 

 both sides, as in this instance onlj' was anj' marked asymmetry observed. 



Fig. 1. Stage I. Perameles obesuJ-a (IZ). 



— 2. „ I. Dasi/nrus viverrintis (7"5 mm.). 



3. ,, II. D. viverrinus (^i'bvara.). 



4. „ III. P. nasuta (1 S). 



5. „ IV. P. tutsid-a (2 P). 



Plate II. 



Figures 6-8 represent three views of the wax model of tlie heart and gut of 

 Perameles obesula (10.viii.03) Stage V. The gut is painted white, heart 

 endothelium and arteries red, veins and most of the capillaries blue, and 

 myocardium yellow. 



These three figures were painted by Miss E. A. Steele. 



Fig. 6. Ventral view of model of P. obesula (10.viii.03). 



7. Dorsal view. 



8. Lateral view. 



