Dissection of Common Rat, 205 



Trachea consists of a series of pieces of cartilage, segments 

 of rings, which are connected together by fibrous tissue, each 

 piece of cartilage forming an incomplete ring. By placing a 

 piece under a low power of the microscope, he will further note 

 that between the ends of the cartilages is a continuous trans- 

 verse layer of unstriated muscle, which is attached to the 

 truncated ends and the inner surface of the cartilages, under- 

 lying a few superficial longitudinal fibres. The mucous 

 membrane lining the tube is furnished (when fresh) with a 

 columnar, ciliated epithelium. Again, it will be noted that 

 the right Bronchus is subdivided near the Lung, into as 

 many primary branches as there are lobes, and that in point 

 of position each Bronchus is situated dorsad of the pul- 

 monary arteries and veins. 



If now the Student will make a flat section of one lobe of 

 the Lung, cutting it in the direction of its largest superficies ; 

 and a second, straight through and across the lobe, he will be 

 enabled to see the larger branches of the bronchi, and their 

 mode of branching ; also the blood-vessels, and the general 

 cellular structure throughout. If specially injected and 

 hardened (when fresh), the structural changes in the air- 

 tubes should be examined under a microscope ; the pieces of 

 cartilage seen in the Trachea becoming broken up in the 

 smaller bronchial tubes, and scattered over the wall as ir- 

 regular fragments, and lastly disappearing : the fibrous and 

 elastic tissues of the bronchial tubes being alone continued to 

 the air cells. 



Dissection of Sympathetic Cord, &c., in the Thorax. 

 Yentrad of the spinal column, lying in the interpleural 

 space, are the Aorta, Azygos Veins, CEsophagus, and 

 Splanchnic Nerves, all of which should be traced out. 



If the Student will examine the wall of the Thorax, about 

 a quarter of an inch to the right of the middle line, he will 

 trace a slight seam taking a longitudinal direction. This 



