480 



MISS K. M. PARKER ON THE 



throue-hout its length (PI. II. fig. 7, D.A.). From the anterior 

 convexity of the loop of the first arch there is given off on each 

 side a vessel which runs outwards and forwards and then breaks 

 up into series of capillaries which form a cup surrounding the 

 primary optic vesicles. These capillaries run round the postero- 

 lateral face of the optic vesicle to become connected dorsally 

 with the veins of the head (fig. 7). 



The second aortic arch arises from the dorsal side of the bulbus, 

 runs backwards and outwards to loop round the gut in the hyoid 

 arch and to join the dorsal aorta (see PI. II. figs. 6-8, A. 2). 



From the dorsal aort« posterior to the second aortic arch, 

 there arises a pair of small sprouts running outwards on the gut- 

 wall. These are the dorsal elements of the third aortic arch. 



The best developed venous trunk of the head, viz. the vena 

 capitis medialis, is clearly seen in the dorsal view of the model 

 (fig. 7, V. CM.). Each is a small vein lying dorsal to the dorsal aorta 



Text-figure 19. 



/ici/. 



Ferameles obesula (10.viii.03). Transverse section througt the Cuvierian ducts. 



A.C.V. Anterior cardinal vein. CD. Cuvierian duct. B.A. Dorsal aorta. Mid. 

 Endothelium. 3£.P. Medullary plate. If.y. Myocardium. V.C.M. Vena 

 capitis medialis. 



close against the neural tube (text-fig. 17, V.C.M.). Anteriorly 

 this vein runs into the dorsal aorta. In the model this is only 

 shown on the left side, but high-power examination of the 

 sections reveals a very fine capillary completing the connection 

 between the right vein and the aorta. Arising from the vena 

 capitis medialis in the anterior half of the mandibular arch is a 

 series of capillaries which are continuous with those surrounding 

 the optic vesicles. The brain here is widely open and its margin 

 is situated just to the outer edge of the capillaries. The latter 

 would accordingly lie medial to the neural crest were such present 

 in this region. In the region of the first visceral pouch there is 

 another line of capillaries lying lateral to the vena capitis medialis 

 and connected with it. From the anterior end of these capillaries 

 there runs outwards and forwards a vessel connecting them with 

 a group of capillaries lying in the mandibular mesoderm lateral 



