BLOOD-VASCFLAR SYSTEM OF THE TILE-FISH. 



91 



arch, and run mesad; the first and second pairs unite to form the first aortic root (fig. 4, 

 ,1/'. /). while the third and fourth similarly unite to form the second [Ar. ..'). The 

 aortic roots of each side unite in the median line, ventral to the first vertebra, to 

 form the dorsal aorta. The posterior arc of the circulus cephalicus is formed on the 

 base of the skull by the proximal portion of the tirst pair of efferent branchial arteries 

 and the first pair of aortic roots. In 

 frontthe circulus is completed by the 

 union of the internal carotids. 



Kidewood (1899) has classified 

 the circulus cephalicus of teleostsinto 

 four groups. A. 15. C, and I>. on the 

 basis of the relationships held by 

 the efferent branchial arteries to the 

 circulus and the dorsal aorta. The 

 groups A, B, and D are represented 

 by Pomolobus (tig. 3). Leptocephalvs 

 (fig. 2) and MZcrogadw (fig. 9), re- 

 spectively. The tile-fish would fall 

 under group C, since the first and 

 second efferent branchial arteries 

 open into the circulus cephalicus and 

 the third and fourth open into the 

 aorta immediately behind the cir- 

 culus (fig. 1). 



ARRANGEMENT OF THE BRANCHIAL 

 VESSELS ON THE GILL ARCHES. 



Tin: efferent vessels. — The efferent 

 branchial arteries are usually split for 

 some distance at their ventral ends 

 (tig. 12), the two branches lying one 

 on each side of the afferent trunk. 

 For the most part the efferent tila- 

 mentar arteries open directly into 

 the efferent trunk; the most dorsally situated, however, communicate with it by 

 means of two collecting vessels (#, figs. 5 and 18), one from each hemibranch. (In 

 a specimen 50 cm. long, these collecting vessels measured 1 to 3 cm. in length.) So 

 far as known to the writer, the efferent branchial vessels of teleosts have been 

 described as single, one vessel on each holobranch and the two series of filamentar 

 vessels opening into it. Parker (1886, p. <i89) states as follows regarding the efferent 

 branchial vessels: "In Holocephali and Teleostei there is only one efferent artery to 

 each gill, corresponding to the anterior of the two efferent arteries in the plagiostome 

 holobranch." The writer finds, however, in a large number of teleosts in addition 

 to the tile-fish, indications of two efferent branchial arteries on a single arch. In 

 some instances these vessels are double for almost the entire length of the arch, as 

 in the case of the conger eel (Zeptocephalus, tig. 2), thus resembling in many respects 

 the corresponding vessels in Ceratod-us, described by Spencer (1893). 



Fig. 2.— Efferent branchial and heart arteries, with circulus cepha 

 lieus, in the conger eel (Leptocephalus conger). Ventral aspect, 

 natural size. On the right sirte the efferent branchial vessels 

 are shown reflected so as to bring them into one plane. The 

 ventral ends of the left efferent branchial arteries are drawn to 

 show their relation to those of the opposite side. 



