X PRACTICAI. DIRECTIONS 535 



precaval and postcaval veins ; c, the Eustachian vaive ; a, the apeitui e 

 of the coronary vein witliiii the tunnel-likc opening of the left precaval ; 

 f, the apertures of tlie pulmonary veins. 



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

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

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

 ventricular apertures, and squeeze the ventricles, noting — 



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

 the origuis of the aorta and pulmonary artery respectively ; h, the aper- 

 tures of the coronary arteries just on the distal side of 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 extrem- 

 ities, 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 ventriculorum, the cavities of the two ventricles, 

 and the muscular ridges in their walls. • 



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

 cords and papillary muscles. 



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: Nolice ihe A/eiiomian glands {p. 518). Cut away, with bone 

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

 any of the contents of the orbit. Note — 



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

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

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

 large infraorbital gland, lying mainly within the orbit below (p. 495). 



2. The four recti and the two oblique muscles of the eye. Note the 

 course of the superior oblique through its tendinous loop (p. 517). 



3. The lachrymal and Harderian glands, situated in the postero- 

 superior and antero-inferior regions of the orbit respectively. 



II. Remove the eyeball by cutting through the muscles and optic nerve. 



