Dissection of Common Rat, 201 



Lung, the (Esophagus passes, as above noted : dorsad of the 

 CEsophagus, close to the back and slightly to the left of the 

 median line, being partially hidden by the left lobe of the 

 right Lung, will be found the Aorta, of which the abdominal 

 portion (up to the Diaphragm) has been previously traced : 

 and lastly, in the anterior portion of the Thorax, coming away 

 from between the ventral aspect of the spinal column, and 

 the Aorta, will be seen the Vena Azygos of the left side, 

 which, after passing round the root of the left Lung, joins the 

 left vena cava descendens. 



The stratification of the three chief sy sterns of the body may 

 be here noted, and should be well borne in mind, for it is 

 characteristic of all Yertebrata to have the Vertebral column 

 tvith its cotitained nervous system dorsal, the Heart ventral, and 

 the Digestive system intermediate to the other two. 



Dissection of Vessels and Nerves in the middle line 



BETWEEN THE CUT ENDS OP THE FlRST AND SeCOND RiBS ON 



EITHER SIDE. The Heart lies opposite the middle of the 

 Sternum, its longitudinal axis inclined obliquely from above 

 downwards, slightly backwards and to the left : being, as it 

 were, dependent from the vertebral column ; consequently, 

 the apex alone comes near the Sternum. 



By cleaning carefully the vessels at the anterior part of 

 the base of the Heart, their relative positions will be found to 

 be as follows : to the right, the right vena cava descendens ; 

 and next, the commencement of the arch of the Aorta (not 

 colored by the injection), from which a branch proceeds 

 straight forwards between the vena cava and the Trachea, 

 which is the Innominate Artery. This Artery should be traced 

 forwards with great care to about opposite the cut end of the 

 first rib, where it will be found to bifurcate, one branch con- 

 tinuing onwards as before, which is the right common carotid ; 

 the other branch bending under the point of junction of the 



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