582 



treme anterior end of the median dorsal aorta. Posterior to this 

 vessel the epibranchial prolongations of the efferent arteries of the 

 third and fourth branchial arches fall separately and independently 

 into the median dorsal aorta. This is exactly as shown by Hyrtl 

 in his figures of Eaja clavata and Torpedo narke, the three vessels 

 that thus fall into the median dorsal aorta being, respectively, the 

 anterior, middle and posterior aortal roots of his descriptions. In 

 Eaja nasuta a similar arrangement of these arteries is also doubtless 

 found, but they are not so shown in either of Parker's two figures of 

 the arteries in this fish and the arrangements shown in those two 

 figures differ markedly one from the other, as will be later explained. 



From the so-called anterior aortal root, in Eaja radiata, a small 

 artery has its origin and after sending branches to the tissues adjacent 

 to the anterior vertebral plate perforates that plate to enter the spinal 

 canal and there fall into the myelonal artery. This small artery, which 

 thus has definitely certain characteristics of a vertebral artery, is the 

 artery "vr" (vertebral artery) of Parker's Fig. 20 of Eaja nasuta, 

 and the so-called arteria musculo-spinalis anterior of Hyrtl's des- 

 criptions; and Hyrtl says that the ramus spinalis of this artery 

 enters the spinal canal and was considered by Johannes Müller 

 and other authors of the period as the carotid posterior. From the 

 efferent glossopharyngeus feeder of the first aortal root, in Eaja 

 radiata as in Eaja clavata, the arteria temporo-maxillaris of Hyrtl's 

 descriptions has its origin, and runs downward in the hyoidean arch 

 somewhat in the position of an anterior efferent artery of that arch. 

 This artery is not shown in Parker's figure of Eaja nasuta. 



The anterior aortal root, above described, is certainly formed 

 by that portion of the lateral dorsal aorta of its side that lies posterior 

 to the efferent first vagus artery, and it forms, on either side, the 

 posterior portion of the circulus cephahcus of the fish, this portion 

 of the circulus being continued anteriorly by that section of the lateral 

 dorsal aorta that lies between the efferent first vagus and efferent 

 glossopharyngeus arteries and then by the epibranchial portion of the 

 latter artery, as I have already shown it in a diagrammatic figure 

 of the arteries of this fish (Allis, 1908, Fig. 5). But this interpre- 

 tation of the composition of this vessel is not strictly in accord with 

 what Dohrn says of its development. On page 41 1 of his XV study 

 (1890), when discussing the hyoideo-glossopharyngeus section of the 

 lateral dorsal aorta, his so-called "Verbindungsstück zwischen Carotis 



