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fifth and sixth gill loops, it is connected with its fellow of the opposite 

 side by a cross-commissural vessel that passes dorsal to the truncus 

 arteriosus ; and at or near the point of origin of the posterior one of these 

 three cross-commissures, a branch is sent outward anterior to the 

 sixth afferent branchial artery, this branch being so important that 

 it appears as the direct posterior continuation of the main vessel. 

 This ventral branch, having passed beyond the line of the afferent 

 arteries, turns posteriorly, ventral to the sixth afferent artery, and 

 lying along the ventro-lateral aspect of the truncus arteriosus reaches 

 and supplies the heart, being there connected with its fellow of the 

 opposite side by annular commissure. This ventral branch is accor- 

 dingly the coronary artery of the fish. From this coronary artery, 

 not far from its origin, a delicate branch is given off which is quite 

 certainly the homologue of the hypobranchial artery of Parker's 

 (1886) descriptions of Mustelus, but the head of my fish had been cut 

 off so short that the artery could not be traced to the subclavian. 

 In Mustelus antarcticus, Parker describes a well developed, 

 so-called median azygos hypobranchial and from this artery the 

 coronary arteries are said to have their origin. The azygos hypo- 

 branchial is said to receive two commissural vessels, on either side, 

 from a longitudinal vessel, the so-called commissure 1, that unites 

 the ventral ends of the efferent branchial arteries, these two commis- 

 sural vessels arising from the longitudinal vessel between the efferent 

 gill cleft loops and not from those loops, as in Heptanchus. This 

 longitudinal commissure, in Mustelus, is evidently the homologue 

 of the longitudinal vessel that I have described in Heptanchus, but 

 the vessel in Heptanchus lies internal, that is dorso-mesial to all the 

 afferent branchial arteries, while in Mustelus it is shown external 

 (ventro-lateral) to the afferent branchial arteries in Parker's Fig. 1, 

 PI. 34, and internal (dorso-mesial) to those arteries in Fig. 2, PI. 34. In 

 Boulenger's (1904) figure of this same fish, said to be " after T. Jef- 

 fer Y Parker", it is shown lying external to the hyoidean and first 

 branchial afferent arteries but internal to the more posterior afferent 

 arteries. These differences, in these several figures, in the relations 

 of these arteries to each other, I did not notice when making a dia- 

 grammatic figure of the arteries of Mustelus, in connection with an 

 earher work (Allis, 1908), and I there placed the longitudinal vessel 

 external to the afferent arteries, as shown in Parker's Fig. 1 ; but 

 this is quite certainly not the normal arrangement, if it be not wholly 



Anat. Anz. Bd. 41. Aufsätze. 31 



