242 AN INTRODUCTION TO ZOOLOGY 



which they give off numerous afferent renal branches and getting 

 smaller and smaller disappear at the anterior end of these bodies, 

 into which all their blood is poured. Between the kidneys the posterior 

 cardinal sinuses take origin as a median unpaired trunk formed by 

 the running together of a number of efferent renal veins. The 

 median trunk, however, is completely separated into two by a 

 membranous septum as it passes forward from the front end of 

 those glands under the peritoneum on the dorsal side of the coelom. 

 About half-way forward to the pericardio-peritoneal septum their 

 partition disappears, and thereafter is only represented by a few 

 bands of tissue. At the same point they receive a median genital 

 sinus coming from the gonads, and in its turn receiving a vein from 

 the right side of the intestine. The post-cardinal sinuses as they 

 pass forward broaden out considerably until a little further on they 

 occupy the whole of the dorsal width of the ccelom, and they reach as 

 far as the pericardio-peritoneal septum. The blood from the muscles 

 and skin on the dorso-lateral side of the fish is collected up by a 

 lateral cutaneous vein which runs forward from the end of the tail 

 under the lateral line in the septum between the, epi- and hypaxial 

 myotomes. At the level of the hinder end of the pectoral fin it 

 dives down into the muscles and swells out to form a sub-scapular 

 sinus lying on the internal lateral side of the scapular end of the 

 pectoral girdle. This sinus opens into the antero-lateral edge of the 

 post- cardinal sinus by an opening that is somewhat difficult to make 

 out. 



The blood from the pelvic fin and cloacal region is collected by a 

 small iliac vein on each side and conveyed to the dorsal side of the 

 pelvic cartilage, where it anastomoses with its fellow across the 

 cartilage and continues forward as a distinct lateral abdominal vein 

 in the ventro-lateral wall of the coelom just beneath the peritoneum. 

 It reaches the pericardio-peritoneal septum and turns sharply in 

 it, dorsally and mesially along the posterior edge of the coracoid 

 cartilage. A short distance along this it is joined by the large 

 brachial sinus which comes in from the posterior border of the 

 pectoral fin, and the trunk formed by the union of these two vessels 

 is termed the sub-clavian vein. This vessel is a short trunk entering 

 the ductus Cuvieri, as we have noted previously, by an opening 

 common to it and the inferior jugular sinus. 



Thus we have now accounted for the collection of the blood from 

 all regions of the body save the alimentary canal, and this is dealt 

 with, as in the frog, by a special hepatic portal system composed of 

 a number of factors. It starts as a small vessel, the rectal vein, on 

 the ventral side of the rectal gland, and this continues as the posterior 

 intestinal vein up the dorso-lateral wall of the intestine to the level 



