MORPHOLOGICAL STUDY OF TRACHEAL AND BRONCHIAL CARTILAGES. 297 



and in expiration the curved processes extending along each bronchus serve to sup- 

 port them in an efficient manner and to prevent their collapse. 



In figure 22 we have two saddle-shaped cartilages placed, one on the ventral 

 side, the other on the dorsal side of a small bronchus which is directed anteriorly. 

 In figure 6 only the anterior cartilage can be seen, but in figure 22 the anterior and 

 mesial side of each cartilage is shown. Each cartilage has two pairs of processes, 

 the posterior of which fits over the main bronchus, while the anterior extends along 

 the smaller bronchus. Between each anterior pair of processes there is a deep 

 concavity which allows the bronchus to have a dorsal and a ventral movement but 

 does not permit as much freedom of movement in a lateral direction. This type of 

 cartilaginous support is intermediate between the simple saddle-shaped cartilage 

 and the ring-like cartilage of the succeeding type. 



The first dorsal branch of the main stem bronchus going to the right lobus 

 inferior (fig. 13) is surrounded by an exceedingly interesting cartilage. Its shape 

 is best seen in figure 23, which shows a portion of the main bronchus and a portion 

 of the dorsal branch with the cartilage in situ. The cartilage is quite irregular in 



FIG. 11. A typical saddle-shaped cartilage situated at the first division of the main stem bronchus in the left lobus inferior. 

 A shows the cartilage in situ when seen from the dorsal side; B when seen from the ventral side; C shows the carti- 

 lage alone. X30. 



shape and its two ends are placed, one slightly above the other, directly behind the 

 dorsal branch. These ends do not fuse with each other, neither are they in direct 

 contact. The opening through which the dorsal branch passes is ample and permits 

 free movement of the bronchus in any direction. Another example of this type of 

 cartilage can be seen surrounding the first dorsal branch of the left stem bronchus 

 (fig. 13). With slight modifications I have found this type constantly associated 

 with these bronchi. 



In roentgenograms of the human lung a circular density is not infrequently 

 noted where a branch is given off from one of the larger bronchi. This is quite often 

 seen in what may be termed the middle zone (third) of the lung and is usually 

 explained as being due to a bronchus which opens directly towards or away from 

 the observer. That this is occasioned by the bronchus alone is not borne out by my 

 own experience; for I have found it due to either a circular cartilage (figs. 23 and 24) 

 or to two saddle-shaped cartilages (fig. 22). In either instance the bronchus must 

 be viewed in the manner described above in order to produce the circular density. 

 Bronchial cartilages, even in normal lungs, often show a slight calcification, and 



