44 THE NECTURUS 



locate the vessel extending forward from the first efferent 

 branchial artery. This is the internal carotid. Note the 

 parts supplied by this vessel. 



Vertebral Artery 



At this point in the dissection the vertebral artery is 

 easily determined. It extends anteriorly from the base of 

 the roots of the aorta. It is seen as a branching artery 

 mesial to the internal carotids. A small branch goes to 

 the posterior along the vertebral column. 



The roof of the mouth is to be studied when the cut is 

 made to locate the internal carotids and the internal 

 jugulars. Spread the jaws apart and note the structures 

 of this region. 



Small conical teeth are located on the margins of the 

 jaws. Break off a tooth and examine it with a lens of low 

 power, one of three diameters magnification is sufficient for 

 this purpose. 



Locate the external nares and probe through to the 

 posterior nares. They are external to the last row of teeth. 

 Compare the position of posterior nares with those of the 

 frog. The gill slits are two in number and are found on the 

 side of the pharynx. These slits have toothed projections 

 like those found in fishes. The gills, which are external, 

 are attached to the cartilaginous gill arches. These external 

 gills are not homologous with those of fishes. To avoid a 

 destruction of parts, study the lower part of the pharynx 

 and glottis after the dissection of the blood vessels. 



The veins that open into the ductus Cuvieri are the 

 internal and external jugulars, the posterior cardinal, the 

 lateral, and subclavian. 



To follow the jugulars, it is necessary to remove the 

 lining of the inside of the mouth and to expose the bases 

 of the gills on the dorsal side. 



