SCYLLIUM 61 



gill-slit and joining above it. Each gill- arch therefore contains 

 two such vessels and one afferent vessel. The demib ranch 

 of the 5th gill- slit is drained by the 4th efferent branchial 

 artery. The demibranch of the spiracle receives already 

 oxygenated blood from the anterior demibranch of the 1st 

 gill-slit. Since it does not oxygenate this blood itself it is 

 called a pseu dob ranch. The vessel leading from it to the 

 internal carotid inside the skull is the efferent pseudobranchial 

 artery, which can be seen at the back of the orbit or eye-socket. 



The anterior prolongation of the dorsal aorta is the internal 

 carotid artery which pierces the base of the skull and supplies 

 the brain. The dorsal aorta gives off paired subclavian 

 arteries to the pectoral fins. Into the mesentery suspending 

 the gut it sends the following : cceliac, lieno-gastric, anterior 

 and posterior mesenteric arteries, which between them 

 vascularise the stomach, liver, intestine, and the well-developed 

 spleen. Farther back the dorsal aorta gives off pelvic arteries 

 to the pelvic fins and renal arteries to the kidneys as well as 

 branches to the gonads, and continues into the tail as the 

 caudal artery. The blood from the tail is returned forwards 

 by the caudal vein which forks, one branch going to each 

 kidney as the renal portal vein. From there the blood is 

 removed by the posterior cardinals. 



Ductless Glands (see Chapter XXXIII). — The spleen has 

 already been mentioned ; it lies in the mesentery near the 

 stomach (see p. 152). 



With the development of jaws, the ciliary mode of feeding 

 has been abandoned. The wheel- organ of Amphioxus is 

 represented by an ectodermal ingrowth — the hypophysis, 

 which comes into intimate contact with the infundibulum of 

 the brain to form the pituitary body. 



Fig. 32. — Scyllium : diagrammatic view of the arterial system, and of the 

 sympathetic, supra-renals, and inter-renal (female specimen). Partly 

 from a drawing by Mr. J. Z. Young. 



c, caudal artery ; Ca, cceliac artery ; da, dorsal aorta ; eb 2, second 

 efferent branchial artery; ep, efferent pseudobranchial artery; gi, first 

 gill-slit ; ia, iliac artery ; tc, internal carotid artery ; ir, inter-renal body ; 

 k, mesonephric kidney ; s, spiracle ; sa, subclavian artery ; sg, sympathetic 

 ganglia, some of which are interconnected by the longitudinal sympathetic 

 nerve-chains ; sr, supra-renal bodies. 



