Pseudobranchial and Carotid Arteries in the Gnathostome Fishes. 105 



external to the other; and as the efferent artery, lying' deeper in 

 the arch, has an apparently anterior position , and as it is said to 

 actually be the anterior artery in teleosts (Parker, 1886, p. 689), 

 I so placed it in Amin. 



In the accompanying- Fig. 1, the vessels in young embryos of 

 Pristiurus and Scyllium are shown, as given by Dohrn (1885 and 1890). 

 The efferent g-lossopharyngeal artery has anterior and posterior branches, 

 and the artery is shown as wliolly separated from the afferent 

 artery, instead of still being" connected w-ith that artery, as Dohrn 

 gives it. The anterior and posterior branches are connected by 

 three commissures, two intermediate and one dorsal, the latter 

 commissure connecting the branches with the main efferent, or epi- 

 branchial artery. 



In tlie hyoidean arch the posterior branch of the efferent artery 

 is alone found, and this branch is connected by commissure with 

 the artery of the mandibular arch; the commissure joining the latter 

 artery betw^een the sections called by Dohrn the thyreo-spiracularis 

 and afferent spiracular arteries. Slightly dorsal to the gill-filaments 

 in the hyoidean arch, and hence probably at the point where the 

 dorsal commissure would normally be found, the efferent artery of 

 the arch is said to bend sharply forward; and from this point 

 onward the artery is described by Dohrn as the posterior carotid. 

 In later embryonic stages than that shown in the diagram, a 

 commissure is said to develop between the hyoidean and glosso- 

 pharyngeal aortic arches, this commissure extending backward from 

 the sharp bend in the hyoidean artery. Where the commissure 

 joins the efferent glossopharyngeal artery is not stated, but I assume 

 it to be at the point where the anterior and posterior branches of 

 that artery are united by dorsal commissure; for that is the point 

 where the commissure joins the artery in the adult Mustehis ant- 

 arcUcus (Parker, 1886). After this commissure has developed, that 

 section of the aorta that lies between the dorsal ends of the hyoidean 

 and glossopharyngeal efferent arteries is said to become relatively much 

 reduced in all selachians (apparently not in Chlamydoselaclms, Aters, 

 1889), and to wholly abort in all the Batoidei. 



From the efferent hyoidean artery, just before it joins the 

 dorsal aorta, or from the latter artery slightly anterior to the 

 hyoidean aortic arch — Dohrn's two figures and his descriptions 

 not agreeing in this — , a small branch is said to be given off; and 



