IOO 
MAMMALIAN ANATOMY 
the dorsal midline. Above each fold is an elongated depression, 
the ventricle, which is bounded anteriorly by the ventricular 
fold. Note that while the vocal folds are approximated and 
stretched into the position for vocalization of the breath by the 
contraction of the cricothyreoid muscles which pull forward upon 
the thyreoid cartilage, the tension of the vocal folds is regulated 
by the various combinations of contractions of the other muscles 
of the larynx, which are inserted, as shown by the above dissec¬ 
tion, into the muscular processes of the arytamoids. Draw the 
interior view of the larynx. 
C. THE HEART AND LARGE BLOOD VESSELS. 
Remove the loose pericardial sac which surrounds the heart, 
noting that a reflected portion of the pericardium fits tightly to the 
heart and forms its outer layer. By palpation and by external 
examination locate the four chambers of the heart (i.e., right 
auricle and ventricle, and left auricle and ventricle), and identify 
the blood vessels connected with each. Draw dorsal and ventral 
views. 
Make a cross section near the apex of the heart to demonstrate 
the circular form of the cavity of the thick-walled left ventricle, 
and the crescentic form of the cavity of the thin-walled right 
ventricle. Note the tendinous attachments of the tricuspid and 
bicuspid (mitral) valves in the right and left ventricles, respec¬ 
tively. By probing, show that the pulmonary artery leads from . 
the right ventricle and the aorta from the left. 
Taking care to avoid the anterior and posterior venae cavae 
which open into the right auricle, make a longitudinal slit through 
the wall of both the right auricle and right ventricle, thus laying 
open the two cavities. Note the thin, distensible walls of the 
auricle, the place of entrance of the veins, the auriculo-ventricular 
orifice through which the blood leaves the auricle and enters the 
ventricle and the tricuspid valve which guards this orifice. Draw. 
Make a similar dissection of the left side of the heart, noting 
the entrance of the pulmonary veins into the auricle, and the 
bicuspid valve guarding the auriculo-ventricular orifice. 
Make an incision transversely through the pulmonary artery 
about an inch above the heart and look down toward the heart to 
