Nos. IAXD2.] AX ATOMY OF SCOMBER SCOMBER. 149 



The efferent artery of the first (ca, I, Figs. 59 and 60), as it 

 reaches the dorsal end of its arch, Hes along the antero-dorsal 

 aspect of the suprapharyngeal process of the epibranchial of its 

 arch, immediately anterior both to the external levator of the first 

 arch and to the anterior division of the internal levator of the 

 arches. When it reaches the dorsal surface of the suprapharyngo- 

 branchial of the first arch it turns sharply backward, passes ventro- 

 internal to the trunk of the first vagus nerve, and is joined by 

 the efferent artery of the second arch. The single trunk formed 

 by the two arteries so united then turns postero-mesially and joins 

 the anterior end of the dorsal aorta. The eft'erent artery of the 

 second arch, as it reaches the dorsal end of its arch, lies posterior 

 to the first vagus nerve, anterior to the external levator of the 

 second arch, and in the angle between the anterior and posterior 

 divisions of the internal levators of the arches. 



Opposite the proximal end of the epibranchial of the fourth arch 

 the efferent arteries of the third and fourth arches join the dorsal 

 aorta, the two arteries there being somewhat united in a common 

 trunk. The artery of the third arch lies anterior to the external 

 levator of its arch and ventral to' the obliquus dorsalis of the arch. 

 The artery of the fourth arch lies dorso-posterior to all the muscles 

 of the arches excepting only the so-called fifth externus muscle. 



The eft'erent artery of each of the arches receives, at the point 

 where it leaves the proximal end of the grooved dorsal surface 

 of the epibranchial of its related arch, a branch that comes from 

 that part of the gill of the arch that lies anterior to that point. The 

 cut ends of these branches are seen in the figures. 



The common carotid artery (cc, Fig. 60) arises from the dorsal 

 surface of the efferent artery of the first arch, at the point where 

 that artery bends sharply backward to join the efferent artery of 

 the second arch. Running upward and forward, in front of the 

 nervus glossopharyngeus, it soon separates into its two portions, 

 the external and internal carotids. The former continues for a 

 short distance the direction of the common carotid, and then turns 

 sharply forward, and, lying ventral to the jugular vein, enters the 

 posterior opening of the trigemino-facial chamber in the petrosal, 

 its further course not being traced. The internal carotid turns 

 sharply downward and then forward, and, passing mesial and 



