54 PRACTICAL HISTOLOGY. 



TRANSVERSE SECTION OF TRACHEA OF A CAT. 

 Stain it for half an hour in picrocarmine and mount in Farrant's solution. 



EXAMINATION (L). Observe the arc of hyaline cartilage forming nearly two-thirds of a 

 circle and deficient posteriorly. The cartilage is invested by a fibrous perichondrium stained 

 red. It is continuous with the layer of circularly disposed non-striped muscular fibres, that 

 connect the ends of the cartilages and help to make up the posterior wall of the trachea. This 

 muscle, the trachealis muscle, is not inserted into the tips of the cartilage-rings, but into the 

 outer surface of the fibrous perichondrium, some distance from their free ends. The muscle is 

 easily made out, for it has a dull red appearance. Outside the cartilage is some fat and con- 

 nective tissue. Observa the mucous membrane with its columnar ciliated epithelium, and under 

 it the submucous coat, containing many mucous glands, most of the acini of which lie internal 

 to the cartilages, and it may be some adenoid tissue. The sacs of each mucous gland are en- 

 closed in a connective-tissue capsule, and have a flattened appearance where they lie inside the 

 cartilage, but are round or oval between the rings. Between the different groups of glands 

 single fat-cells, or small groups of fat-cells, may be seen. {Indicate the general cliaracters in 

 PL X., Fig. i.) 



(H). Observe the epithelium in several layers, the upper layer cylindrical and ciliated. It 

 rests on a basement-membrane not easily seen in the trachea of the cat, though easily seen in 

 the human trachea, where it plays an important role in pathological processes. Amongst the 

 epithelium are goblet-cells which are stained of a deep red. Under the epithelium observe 

 beautiful layers of elastic fibres arranged longitudinally, which appear as rows of bright 

 yellow dots lying amongst the connective tissue. Observe the mucous glands, and their acini 

 inside the cartilages, and trace a duct to its opening on the surface in a funnel-shaped manner. 

 The acini of the glands lie in the submucous coat, which in addition to connective tissue con- 

 tains a very considerable quantity of adenoid tissue. As the gland-ducts pass obliquely to 

 reach the surface, it is difficult to get a complete section of a gland with its excretory duct. 

 The ciliated epithelium is continued a short distance into the excretory duct, but it soon gives 

 place to moderately tall cylindrical epithelium, which lines the duct. The alveoli or sacs of 

 the gland vary in appearance according to whether they were or were not secreting at death. If 

 secretion had been taking place, the cells lining them will be filled with a clear transparent 

 mucus-like mass, and few granular cells are to be seen. If there has been no secretion, the 

 gland-sacs will be lined by a regular cubical epithelium of a more or less granular appearance. 

 Observe the numerous leucocytes in the submucous coat. Observe the non-striped muscle 

 trachealis only present posteriorly and its attachment to the perichondrium some distance 

 in front of the free ends of the tracheal rings. Outside it may be seen transverse sections 

 of nerves and nerve-ganglia. As the mucous membrane is very vascular, many sections of 

 blood-vessels will be seen in it. The cartilage is ordinary hyaline cartilage, but its corpuscles 

 present a characteristic arrangement. Under the perichondrium the cells are flattened, and lie 

 parallel to the surface of the cartilage, whilst those in the interior are elongated or oval and are 

 placed vertically from one surface to the other, i.e. across the long axis of the cartilage. (Indi- 

 cate the epitlielium, glands, and part of the cartilage in PI. X., Fig. 2.) 



Double-stain a section of a trachea with picrocarmine and iodine green (p. xlv). The mucous 

 glands, adenoid tissue, and cartilage are stained green. 



Vertical section of Trachea, stained with picrocarmine and mounted in Farrant's solution. 



EXAMINATION (H). Observe the elliptical pieces of cartilage the sections of the car- 

 tilaginous rings cut vertically. Observe the same general arrangement as described in the 



