552 THE RABBIT CHAP. 



4. Note a, the thyroid gland ; b, the thyroid and cvicoid 

 cartilages of the larynx ; c, the brachial and vertebral 

 branches of the subclavian artery ; and d. the brachial 

 plexus (p. 532). 



IV. Remove the heart and lungs from the body, together 

 with the posterior end of the trachea and recognisable 

 portions of the aorta, precaval, and postcaval. Fasten out 

 the organs under water with their ventral surface uppermost, 

 and after making out the course of the pulmonary arteries 

 and veins, cut through them close to the lungs and separate 

 the latter from the heart. Note : 



1. The two main lobes of each lung and the two accessory 

 lobes on the right side. 



2. The cartilages of the trachea and bronchi ; trace the 

 bronchi for a short distance into the lungs. Sketch. 



V. Cut away the outer walls of both auricles so as to 

 expose their cavities, taking care not to injure the veins 

 which enter them. Wash out the contained clots of blood, 

 and note 



1. a, The appendix of each auricle, and the network of 

 muscular bands in its walls ; b, the septum auricularum and 

 fossa ovali s (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 Ettstachian valve ; 

 d, the aperture of the coronary vein within the tunnel-like 

 opening of the left precaval ; e, the apertures of the pul- 

 monary 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 pulmonary artery ; pour water into 

 the ventricles through the auriculo-ventricular apertures 

 and squeeze the ventricles, noting 



3. a, The bicuspid and tricuspid 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 extremities, 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. 



