THE ANATOMY OF POLYPTERUS. 



333 



thick-walled, deeply-pigmented, coronary vein, which runs free in the pericardial 

 chamber from the ventricle to the ductus Cuvieri. 



From the dorsal side of the dorsal aorta just behind the junction with it of the 

 second efferent branchial artery there passes outwards on either side a small vertebral 

 artery, which curving dorsally round the spinal column appears to enter the spinal 

 canal. 



Fig. 



I/, lie 



The arterial system of Polypterus. 

 br., brachial ; br.', branch of subclavian to shoulder-girdle ; br.", branch of subclavian which becomes the 

 coronary artery; br. I. II. III. IV. off., branchial afferent I., IT., III., IV.; br. I. II. III. IV.eff., 

 branchial efferent I., II., III., IV.; ca., carotid; ecel., cceliac ; ex.g., external gill; hy.aff., hyoidean 

 afferent; Jiy.eff., hyoidean efferent; hy.eff.', hyoidean efferent branch; jp.a., pulmonary; s.d. 

 subclavian ; sp., spermatic. 



Pollard has pointed out the extremely primitive condition of the dorsal arterial 

 system in Polypterus. The single efferent vessel from each gill-arch uniting with a 

 median dorsal aorta, resembles most the condition found in Chlamydoselachvs and the 

 embryos of other Selachians. 



3a 2 



