168 JAY ARTHUR MYERS 



highly modified cartilages which have free ends dorsally, but 

 fuse with the pessulus ventrally. 



The cartilages of the bronchi, unlike those of the trachea, are 

 present only as halves of rings. These half -rings form the 

 framework of the lateral bronchial walls. The first half-rings 

 are modified, and are attached to the pessulus both dorsally and 

 ventrally. The second are only slightly modified and are at- 

 tached ventrally to the first by a small piece of cartilage. Their 

 dorsal ends are free. Certain of these skeletal elements, so 

 briefly referred to, serve as attachments for vibrating mem- 

 branes. The external tympanic membranes (fig. 2) stretch be- 

 tween the first tracheal ring and the first half-ring. First, as 

 used here in reference to the tracheal rings, designates the most 

 caudal, as regards an enumeration of the total number of tra- 

 cheal rings in the caudo-cephalic direction. First, as used here 

 in reference to the bronchial half-rings, has a somewhat dif- 

 ferent meaning. It designates that bronchial half-ring which 

 of all the bronchial half-rings lies in the most cephalic position. 

 These designations are consistently adhered to throughout the 

 paper. The internal tympanic membranes form that part of the 

 medial wall of each primary bronchus which lies immediately 

 caudad to the pessulus. They stretch, therefore, from the 

 pessulus to the cephalic end of the medial membranous wall of 

 each primary bronchus. In fact, the internal tympanic mem- 

 branes may be regarded as specialized portions of the medial 

 membranous walls. Still more caudad to the pessulus and be- 

 tween the caudal extremities of the two internal tympanic 

 membranes, stretching transversely in the medio-lateral plane, is 

 another membrane, the bronchidesmus. From its position, 

 then, the bronchidesmus connects the medial walls of the two 

 bronchi. 



a. Skeletal framework. In the study of the bony and carti- 

 laginous skeleton, three methods were pursued. First, numerous 

 gross dissections were made. Second, cartilage and bone stains 

 were used to stain the organ in toto. For staining bone 2 per 

 cent alizarine in 96 per cent alcohol was used, while j per cent 

 methylene blue in 67 per cent alcohol was employed as a cartilage 



