112 Edward Phelps Allis jr., 



the name given hy Hyktl to a similar vessel said to have been 

 found bj" him in ScyUhtm. This median vessel, described in these 

 two fishes, has been discussed by both Dohrn and Carazzi. and there 

 seems some doubt as to its existence; or, if it exists, as to its being* 

 an arter}^ I have accordingly not given any consideration to it in 

 my diagrams. 



In the adults of Raja (Fig. 5) and Torpedo (Fig. 6) the eiferent 

 branchial arteries are each formed, according to Hyrtl (1858), by 

 the union of the two arteries that lie one anterior and the other 

 posterior to a given branchial slit, this thus being an arrangement 

 similar to that found in Musielus anfarcUcus (Fig. 3). In both Baja 

 and Torpedo, as also in Mustelus antardicus, the two branchial 

 arteries that lie in a given arch are said to be connected by 

 commissure, but whether this commissure is a dorsal one, or an 

 intermediate one, is not evident from the descriptions. I have shown 

 it as an intermediate one, as are the two found in Mustelus. The 

 posterior hyoidean and anteilor glossopharyngeal arteries are 

 connected, both in Raja and Torpedo, by what Dohkn considers as 

 but a single vessel, and he considers this single vessel as the homo- 

 logue of the ventral one of the two vessels that connect the same 

 two arches in Mustelus antarcticus; that is, as a dorsal commissure 

 and not as a portion of the dorsal aorta. While this would seem 

 to be true of Torpedo, where Dohrn (1890. p. 411) says that the 

 hj^oideo-glossopharyngeal section of the aorta is completely aborted 

 even in 12 mm embryos, it may not be true of Raja. For, in the 

 adult Raja, Hyrtl shows this connecting vessel double in its 

 posterior portion, and it seems a proper inference that the two 

 wholly separate vessels of Mustellus may have here, in Raja, simply 

 partially coalesced to form a single branching vessel. 



In Raja the dorsal portions of the aortic arches do not appar- 

 ently differ from those in selachians, but the external carotid would 

 seem, from Hyrtl's figures, to run dorsal to the optic nerve instead 

 of ventral to it. The artery o of Hyrtl's figure of Raja, on his 

 tab. 5, is of course the commissure between the hyoidean and 

 mandibular arteries, and the ai'tery I a part of the afterent man- 

 dibular artery. The efferent mandibular artery is represented in 

 the two vessels lettered I and h, and the arteria ophthalmica magna 

 in the vessel i. The mandibular aortic arch accordingly joins the 

 dorsal aorta anterior to the point where that artery is connected 

 by anastomosis with its fellow of the opposite side, as it does in 



