552 THE RABBIT CHAP. 



bands in its walls ; #, the septum auricularum and fossa ovalis (Fig. 

 139) best seen from the left side by holding the heart between your 

 eyes and the light. 



2. a, the auricula-ventricular apertures; b, the apertures of the 

 precaval and postcaval veins ; c, the Eustachian valve ; a, the aperture 

 of the coronary vein within the tunnel-like opening of the left precaval ; 

 <?, the apertures of the pulmonary veins. 



Then cut away both auricles so as to expose the bases of the ventricles, 

 and remove all but about an eighth of an inch of the aorta and pul- 

 monary artery ; pour water into the ventricles through the auriculo- 

 ventricular apertures and squeeze the ventricles, noting 



3. a, The bicuspid and trictispid valves, and the semilunar valves at 

 the origins of the aorta and pulmonary artery respectively ; b, the 

 apertures of the coronary arteries just distally to the aortic valves. 

 Sketch. 



Now remove the outer walls of both ventricles by making first a 

 transverse incision along the base of each, and then, from its extremi- 

 ties, converging incisions nearly to the apex of the heart. Make 

 out : 



4. The relative thickness of the walls of the right and left ventricles, 

 the form of the septum ventrictdorum, the cavities of the two ventricles, 

 and the muscular ridges in their walls. 



5. The flaps of the tricuspid and bictispid valves, and their tendinous 

 cords and papillary imtscles (Fig. 139). 



6. The apertures of the aorta and pulmonary artery into the left and 

 right ventricle respectively. 



Sketch. 



F. Dissection of the head. 



I. Carefully dissect the skin away from one side of the head ; either 

 side will do, but if you are using the head from which you have already 

 removed the brain, choose the side on which the auditory region is least 

 damaged : notice the Meibomian glands (p. 535). Cut away, with bone 

 forceps, the supraorbital process of the frontal, being careful not to injure 

 any of the contents of the orbit. Note 



i. a, A large mass of muscle (masseter) covering the posterior half 

 of the mandible, on which branches of the facial nerve will be seen ; 

 k, the thin, irregular parotid gland, at the base of the pinna, and the 

 large infraorbital gland , lying mainly within the orbit below (p. 512). 



