MUSEUM OF COMPARATIVE ZOOLOGY. 195 



the branchial apparatus and to the heart. In the saurian Varanus, ac- 

 cording to Wiedersheim,^ (p. 704, Fig. 540, B,) it appears that a por- 

 tion of the ventral aorta (or ventral commissures 1) remains as a single 

 median trunk, from which both the common carotids are given off just 

 ventrad of the hyoidean apparatus, to rise on either side of the throat. 

 The common carotid trunks thus occupy the position of the hyoidean 

 efferent branchial vessels of the Elasmobranch. This common trunk 

 divides above the level of the pharyngeal roof into an external and an 

 internal branch. We thus see that in difiFerent animals the carotids 

 have not the same value in so far as their proximal ends are concerned. 

 The afferent branchial arteries (see Figure 2) number six pairs, and are 

 arranged in sets of two pairs each. While the first two pairs of arteries 

 arise from a common trunk, the arteries of the other pairs arise inde- 

 pendently, with the members of each pair placed opposite each other. 



The anterior innominate artery does not divide into first and second 

 afferent branchial arteries until after it has curved upwards about a 

 quarter of an inch, when the first afferent branchial springs from the 

 anterior edge of the innominate and continues its trunk dorsad, curving 

 gracefully forwards, outwards, and upwards, then considerably backwards 

 to where it enters and suppUes the anterior half of the first gill cleft, or 

 the hyoidean demibranch. The second afferent branchial passes back- 

 wards at an acute angle from its origin at the posterior border of the 

 root of the first, and in its outward and upward course nears the third 

 afferent branchial where the latter enters its arch. 



The sets composed of the afferent branch ials three and four, and five 

 and six, respectively, are so disposed that while five and six leave the 

 synangial end of the ventral aorta, three and four arise from the middle 

 of this trunk. There are slight variations in the size of the vessels 

 forming the pairs two, four, and five, the arteries of the left side being 

 larger than those of the right. The afferent branchials three, four, and 

 five run very nearly parallel with one another, and while the efferent 

 branchials of the pairs three and four continue this relation above the 

 intestine, efferent branchial five bends suddenly backward and fuses 

 with the sixth before entering the dorsal aorta. 



There are six pairs of efferent branchial arteries (see Figs. 1 and 2), 

 corresponding pair for pair with the afferent branchials just described. 

 Only four pairs reach the median dorsal line to form the dorsal aorta ; 

 these are the second, third, fourth, and fifth. The first efferent branchial 



8 Wiedersheim, Robert. Lelirbuch der vergleichenden Anatomie der Wirbel- 

 thiere. Jena, 1885. 



