THE TRACHEA. 263 



Capacity of the auricles and ventricles. — To determine with jirecision the 

 absolute and relative capacities of the four cavities of the heart, as they exist 

 during life, is impossible ; and their capacity is so much influenced by their 

 different states of distension, and also })y the different degrees of contraction of 

 their muscular walls at the moment of death, that no constant numerical relation 

 in this resjiect can be looked for between them. Hence the most opposite state- 

 ments prevail, especially with regard to the size of the ventricular cavities. 



The auricles are generally stated to be rather less capacious than the ven- 

 tricles. The right auricle is also said to be larger than the left, in the i^roportion 

 of ") to 4. (Cruveilhier.) 



The right ventricle is asserted by some to be larger than the left ; by others 

 (Lower, Sabatier, Andral) the two are stated to have an equal capacity ; Cruveil- 

 hier, judging from the effect of injections, has found the left to be the larger of 

 the two. In the ordinary modes of death, the right ventricle is always found 

 more capacious than the left, which is probably owing to its being distended with 

 blood, in consequence of the cessation of the circulation through the lungs : the 

 left ventricle, on the other hand, is found nearly empty, and thus becomes more 

 fully contracted. There are reasons for believing, however, that during life 

 scarcely any difference of capacity exists between the cavities. 



Size of the ventricular openings. — The right auriculo-ventricular opening, 

 and tlie orifice of the pulmonary artery, are both found to be somewhat larger after 

 death than the corresponding openings on the left side of the heai-t. Their cir- 

 cumference is thus stated by Bouillaud. (Traite des Malad. du Coeur, torn. 1. p. 

 52. Paris, 1835.) 



Inches and Lines. 

 Max. Med. Min. 



. . 1 , . , -fi ( Right 4 3 10 3 9 



Aui-iculo- ventricular orinces <T^i. o-./^ o/. oo 



( lieit o 10 6 b •> .i 



Arterial orifices I ^^^^* (Pulmonary) 2 10 2 7 2 6 

 Aiteiial orifices .... JLeft^^o^ic) 28 28 24 



According to observations by Peacock, the average dimensions are somewhat 

 higher : — 



Males. Females. 

 Am-iculo-ventricular orifices \ ?^?!^*^ t I! t .^1 



/Left 3 7 3 10 



Right (Pulmonary) 3 4 3 3 

 Left (Aortic) 3 2 10 



Aiterial orifices j Right (Pulmonary) 3 4 .3 3 



( Lef 



ORGANS OF RESPIRATION. 



Besides the heart, the thorax contains the principal organs of respira- 

 tion, viz., the hmgs and a part of the trachea. The larynx, which is 

 affixed to the upper end of the windpipe, and is not only the entrance 

 for air into the respiratory organs from the pharynx, but also the organ 

 of voice, will be described after the lungs. 



THE TRACHEA AND BRONCHI. 



The trachea or windpipe (fig. 180, fr.), the common air-passage of 

 both lungs, is an open tube which commences above at the larynx, and 

 divides below into two smaller tubes, right and left bronchi, one for 

 each lung. 



The trachea is placed in the median plane of the body, and extends 

 from the lower border of the cricoid cartilage of the larynx (('), on a 

 level with the 5th cervical vertebra in the neck (Gth, Braunc) to a place 

 opposite the 3rd dorsal vertebra in the thorax, where it is crossed in 

 front by the arch of the aorta, and at or immediately below that point 



