MORPHOLOGICAL STUDY OF TRACHEAL AND BRONCHIAL CARTILAGES. 295 



side of the apical bronchus, terminates in a pointed extremity. The lateral arm is 

 the broader of the two, and after arching over the main bronchus and rotating in a 

 manner similar to the mesial arm it passes along the lateral border of the apical 

 bronchus to the posterior border of the main bronchus; it then widens out and, 

 arching around the posterior surface of the main bronchus, continues along its 

 ventral surface to terminate in a pointed extremity lateral to the bar of origin. The 

 point of termination extends beyond the point of origin; the main bronchus is, 

 therefore, surrounded by a cartilage which makes more than a complete spiral 

 turn. This is the best example of a spiral bronchial cartilage which the author has 

 found in any of the animals usually studied in the laboratory. 



Spiral cartilages are frequently found in the Cetacese. Owen gives an illus- 

 tration of a bronchial cartilage from the dugong, which makes four complete turns, 

 but the cartilage is shown of uniform width and regular in its formation, while 

 that above described is irregular in its formation and width and is associated with 

 more than one bronchus. 



On the mesial and dorsal side of the main stem bronchus, opposite to the 

 origin of the bronchus going to the right lobus medius and the bronchus going to 

 the left lobus superior, there are a number of intercalated cartilages which vary in 

 size and shape. These are more numerous on the right side, especially in an area 

 where there appears to be a deficiency in the development of the cartilages. 



In the ventral view (fig. 12) the cartilages supporting these two bronchi are 

 not well shown, but, as was the case with the eparterial bronchus, the dorsal view 

 (fig. 13) shows clearly that in each instance the bronchus is supported by the same 

 type of cartilage as the eparterial bronchus. That this is due to the wide angle at 

 which these bronchi leave their main stem bronchi seems quite probable, for in no 

 other instance do we meet with this type of cartilaginous support, the angle at which 

 the remaining bronchi are given off being much more acute. 



The supporting cartilage of the bronchus going to the lobus medius of the right 

 lung is made up of two broad elements which have a very irregular outline and are 

 perforated by two small openings, which do not give passage to either blood-vessels 

 or nerves. The more anterior of these elements partially encircles the main stem 

 bronchus, but the second element is confined to the dorso-lateral region of the stem 

 bronchus. The supporting cartilage of the bronchus going to the lobus superior 

 of the left lung consists of a single element. Immediately posterior to it, on the 

 dorsal side, is a second cartilage of the same general shape, while on the anterior 

 surface there is a long narrow cartilage which bears the same relation to the support- 

 ing cartilage as the second cartilage on the dorsal side. These two cartilages must 

 be considered as forming a secondary series of supports for the bronchus going to 

 the left lobus anterior. As this lobe is of considerable size and is attached to the 

 main stem by a single bronchus, it undoubtedly requires a strong supporting 

 apparatus, which is supplied by these three cartilages, and they occupy the same 

 relationship to that bronchus as the two fused elements which support the bronchus 

 going to the right lobus medius. 



