22 



_ S.'Dissect out — 

 *sAHOT(a)''The ventral aorta, passing forwards from the synangium. 



(6) The right and left posterior innominate arteries, arising from the root of 

 the ventral aorta, — trace them and note that they each divide into three 

 afferent branchial arteries for the lamellae of the three posterior gill clefts. 



(c) The right and left anterior innominate arteries, arising from the anterior end 

 of the ventral aorta, — note that each divides into two afferent branchial 

 arteries for the lamellae of the first and second gill clefts. 



Note the red coloured thyroid gland situated at the anterior end of the ventral 

 aorta. Make a sketch of the heart and afferent branchial vessels. 



6. CarefuUy expose the gill chambers, and note the hypo-branchial artery crossing 



the afferent branchial arteries, internal to the giUs. Arising from the hypo- 

 branchial artery are the anterior and posterior coronary arteries. 



7. Note that the gill sacs are completely separated from each other by fibrous septa, 



extending from the outer borders of the arches, and that the septa are sup- 

 ported by cartilaginous rays. Observe that the gOl lamellae are attached 

 along their whole length to the septa. 



8. Turn the heart forwards and examine the sinus venosus. Insert a bristle or 



probe into the sinus, and then slit it open. Note that the bristle has passed 

 into the Cuvierian sinus. 



9. Carefully cut away the part of the pectoral girdle over the sinus, and examine 



the venous system, noting the apertures in the Cuvierian sinus of the 

 anterior and posterior cardinal veins, the brachial vein, the hepatic sinus, 

 and on the dorsal side the chief lymphatic trunk. 



10. Pass a bristle along the hepatic sinus, and note that the sinus communicates 



at each end with a Cuvierian sinus, and receives the hepatic veins from the 

 liver. 



11. Pass a bristle along the posterior cardinal veins or inflate with a blow- 

 pipe, and note that the right and left communicate with a median (cardinal) 

 sinus near the centre of the abdominal cavity. From this sinus they pass 

 backwards separately to the posterior end of body. 



12. Trace the brachial veins along the margin of abdominal cavity, and note 



the branches joining them from the pectoral fins. Look for the femoral and 

 iliac veins, and observe, that having united, they again separate into an outer 

 branch (epigastric) which joins the brachial, and an inner branch (ileo- 

 haemorrhoidal) which enters the cardinal sinus. 



13. Note that the caudal vein from the tail divides into two renal portal veins 



which break up in the kidneys. 



