ORGANS OF KKSl'IRATION AND VOICE. 479 



fasciculi which arise from the fibrous rings of the auriculo-ventri- 

 cular openings, and proceed upwards to enlace with each other, 

 and constitute the appendices auriculorum. These fasciculi are 

 parallel in their arrangement, and in the appendices form projec- 

 tions and give rise to the appearance which is denominated mus- 

 culi pectinati. In their course they give off branches which con- 

 nect adjoining fasciculi, and form a columnar interlacement between 

 them. 



External Layer. The fibres of the right auricle having completed 

 the appendix, wind from left to right around the right border of this 

 auricle, and along its anterior aspect, beneath the appendix, to the 

 anterior surface of the septum. From the septum they are con- 

 tinued to the anterior surface of the left auricle, where they separate 

 into three bands, superior, anterior, and posterior. The superior 

 band proceeds onwards to the appendix, and encircles the apex of 

 the auricle. The anterior band passes to the left, beneath the 

 appendix, and winds 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 onwards 

 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 upon the surface of the auricle, others are con- 

 tinued onwards to the base of the aorta; and a third set, forming a 

 small band, is prolonged along the anterior edge of the appendix to 

 its apex, where it is continuous withHhe superior band. The septum 

 auriculorum has four sets of fibres entering into its formation; 1. 

 The fibres arising from the auriculo-ventricular 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 

 fasciculus, 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 

 considerably thicker and more muscular than the right. 



Vessels and Nerves. The Jlrteries 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 by communicating filaments from the sympathetic and 

 pneumogastric. 



ORGANS OF RESPIRATION AND VOICE. 



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



