THE NECTURUS 43 



septum transversum, where they unite to form a single 

 vessel and enter the left auricle. 



Veins Anterior to the Septum Transversum 



Dissect into the anterior part of the sinus venosus and 

 locate the ductus Cuvieri. Several vessels are to be traced 

 to this region, the posterior cardinal, lateral vein, jugular, 

 submaxillary, and subclavian. The anterior end of the 

 post cardinal is seen extending posteriorly. It can now 

 be added to the drawing. At this stage of the dissection 

 work out the vessels connecting with the heart, reserving 

 the heart for later work. 



The study of the afferent vessels is taken up at this point 

 to avoid waste of material. With a slight removal of the 

 muscles at the side of the truncus arteriosus, the afferent 

 vessels appear. Trace these to the gills and note their 

 distribution. After the removal of the skin from the head 

 and gills, the carotids may be dissected out at their origins, 

 with little disturbance to other parts. 



External Carotid 



Remove the skin from the back of the head and the 

 bases of the gills. The external carotid extends anteriorly 

 between the masseter and the ceratohyoid. It is large in 

 comparison with the internal carotid. A short distance 

 from its origin, it branches into several small vessels which 

 supply the orbit, eye, nose, and a part of the jaw muscles. 

 Determine the roots of these twigs. 



Internal Carotid 



Divide the mylohyoid along the median line so as to 

 expose the roof of the mouth. Cut through the symphysis 

 of the mandible so that this region may be fully explored. 

 Dissect away the skin from the roof of the mouth and 



