ORGANS OF RESPIRATION AND VOICE. 485 



of the septum. From the septum they are continued to the anterior sur- 

 face of the left auricle, where they separate into three bands, superior, an- 

 terior, and posterior. The superior band proceeds onwards to the appen- 

 dix, and encircles the apex of the auricle. The anterior band passes to 

 the left, beneath the appendix, and winds as a broad layer completely 

 around the base of the auricle, and through the septum to the root of the 

 aorta, to which it is partly attached, and from this point is continued on- 

 wards to the appendix, where its fibres terminate by interlacing with the 

 musculi pectinati. The posterior band crosses the left auricle obliquely to 

 its posterior part, and winds from left to right around its base, encircling 

 the openings of the pulmonary veins ; some of its fibres are lost on the 

 surface of the auricle, others are continued onwards to the base of the 

 aorta ; and a third set, forming a small band, are prolonged along the 

 anterior edge of the appendix to its apex, where they are continuous with 

 the superior band. The septum auricularum has four sets of fibres enter- 

 ing into its formation ; 1. The fibres arising from the auriculo-ventriculai 

 rings at each side ; 2. Fibres arising from the root of the aorta, which pass 

 upwards to the transverse band, and to the root of the superior cava ; 3, 

 Those fibres of the anterior band that pass through the lower part of the 

 septum in their course around the left auricle ; and, 4. A slender fascicu- 

 lus, which crosses through the septum from the posterior part of the right 

 auriculo- ventricular ring to the left auricle. 



It will be remarked, from this description, that the left auricle is consi- 

 derably thicker and more, muscular than the right. 



Vessels and Nerves. The Arteries supplying the heart are the anterior 

 and posterior coronary. The Veins accompany the arteries, and empty 

 themselves by the common coronary vein into the right auricle. The 

 lymphatics terminate in the glands about the root of the heart. The nerves 

 of the heart are derived from the cardiac plexuses, which are formed b^ 

 communicating filaments from the sympathetic and pneumogastric. 



ORGANS OF RESPIRATION AND VOI'CE. 



The organs of respiration are the two lungs, with their air-tube, the 

 trachea, to the upper part of which is adapted an apparatus of cartilages, 

 constituting the otgan of voice, or larynx. 



THE LA R YNX. 



The Larynx is situated at the fore part of the neck, between the trachea 

 and the base of the tongue. It is a short tube, having an hour-glass form, 

 and is composed of cartilages , ligaments, muscles, vessels, nerves, and 

 mucous membrane. 



The Cartilages are the 



Thyroid, Two cuneiform, 



Cricoid, Epiglottis. 



Two arytenoid, 



The Thyroid (^sog sTSoe, like a shield) is the largest cartilage of the 

 larynx : it consists of two lateral portions, or alee, which meet at an angle 

 in front, and form the projection which is known by the name of pomum 

 Adami. In the male, after puberty, the angle of union of the two alse is 



