MORPHOLOGICAL STUDY OF TRACHEAL AND BRONCHIAL CARTILAGES. 291 



Right bronchial cartilages. -The first bronchial cartilage on the right side 

 forms a smaller segment of a circle than any of the other bronchial cartilages. 

 It ends abruptly on the ventral side of the bronchus near the midline and has two 

 small openings near its mesial end. The second right bronchial cartilage forms 

 nearly a complete circle (fig. 14). The eparterial bronchus is given off just below 

 this cartilage and the third right bronchial cartilage, belonging mainly to the 

 right bronchus, will be considered in connection with its cartilages. 



Left bronchial cartilages. The cartilages of the left bronchus, seven in number, 

 are quite regular in their formation and are placed slightly oblique to the long axis 

 of the bronchus. The first cartilage, as already stated, enters the carina tracheae 



2RB1LB2LB 3LB 



FIG. 5. Section taken through the center of cartilage No. 3 in figure 12. This is a typical tracheal cartilage without any 

 fission or fusion with an adjoining cartilage. The broken line extending from one end of the cartilage to the other 

 indicates the positions of the muscle. Note the internal attachment of the muscle and that it is not inserted into 

 the ends of the cartilage but some distance lateral to them. X6. 



FIG. 6. Sect : on taken along the plane indicated in figure 12. The bifurcation of the trachea into the right and the left 

 bronchus has taken place. R. B., right bronchus. L. B., left bronchus. 1 L. B., lower portion of the mesial arm 

 of the first left bronchial cartilage which forms the carinal cartilage. 2 L. B., second left bronchial cartilage. 

 3L.B., third left bronchial cartilage. 2 R. B., ventral and dorsal section of the second right bronchial cartilage. X6. 



FIG. 7. Outline of a section taken along the line indicated on figure 13, showing the relation of the cartilages to the right 

 bronchus, R. B., and to the left bronchus, L. B. X6. 



and continues for some distance in that structure (fig. 6). The fifth, sixth, and 

 seventh cartilages do not encircle the bronchus as extensively as do the second, 

 third, and fourth cartilages. 



Turning now to a dorsal view of the tracheal and bronchial cartilages (fig. 13), 

 it will be seen that only the left tip of the first tracheal cartilage modeled is visible, 

 and that the mesial end of the first bronchial cartilage on the left side is hidden 

 from view by the expanded end of the second right bronchial cartilage. Of the 

 remaining cartilages the left extremity of the last tracheal cartilage and the mesial 

 extremity of the second right bronchial cartilage attract attention. The former of 

 these is broadly expanded and has a well-marked posterior prolongation (fig. 13); 

 the latter is expanded into an oval plate which fits into the angle between the right 

 and left bronchus. Near the center of this expanded extremity is an oblong fora- 

 men (fig. 14) which gives passage to a small blood-vessel. It will also be noted that 

 where the extremity of a cartilage is expanded the extremity of one of the adjoining 

 cartilages is, as a rule, reduced in size for example, the tracheal cartilages Nos. 

 2 and 4, and the bronchial cartilages Nos. 1 and 3 on the left side. 



Considering the dorsal view of the trachea and bronchi as a whole, it will be 

 noted that the interval between the ends of the cartilages in the trachea, which 

 corresponds to the membranous portion, occupies the mid-line; as this is followed 

 into either the right or the left bronchus it gradually rotates 90 and comes to occupy 

 a mesial portion. 



