18/6.] ANATOMY OF CHAUNA DERBIANA. 193 



to the bronchi, the Screamers are not Anserine, and in the latter 

 feature peculiar. 



There is nothing remarkable in the rings of the windpipe, their 

 interlocking producing the well-known key-pattern. The last two 

 are greatlv compressed laterally, so that the membranous bronchi, in 

 each of which there are only a very few slender half-rings, arise quite 

 close together. As can be seen from the figure, Place XII. figs. 2, 

 3, 4, the lateral muscles of the trachea are peculiarly powerful ; the 

 upper extrinsic pair is inserted into the middle of the membrane 

 which runs between the body of the coracoid bone and the corre- 

 sponding limb of the furcula on each side ; the lower close to the 

 costal process of the sternum, at the back of the sterno-coracoid 

 articular margin of the former bone. The intrinsic muscle on each 

 side descends the windpipe to end by bifurcating opposite the origin 

 of the sterno-tracheal muscle, and cease, its anterior portion higher 

 than its posterior, six or seven rings lower down, some distance above 

 the bifurcation of the bronchi. The above-mentioned extremely 

 delicate nature of the commencing bronchial tubes is most peculiar. 



The lungs present no special features of interest. 



There are several myological characters which, though small in 

 themselves, all go to form the exact definition of any group of birds, 

 and aid in the determination of affinities. Among the more im- 

 portant of these are the presence or absence of the ambiens muscle* 

 (which is of fair size in Chaunci), the presence or absence of the 

 femoro-caudal, the semitendinosus, and their accessory heads (which 

 are all four found in Chauna). Having dwelt fully on the impor- 

 tance of these muscles in the paper just referred to, all I need remark 

 on the present occasion with regard to them is, that there is there- 

 fore a difference between this bird and all the true anserine birds, in 

 none of which is there ever a trace of the accessory semitendinosus. 

 A reference to my paper on the muscles of the thigh of birds will 

 show that in possessing all the five above-mentioned muscles the 

 Screamers agree only with the Gallinas and their nearest allies, the 

 Rallidae, Musophagidae, Cuculidse, Columbse, and some of the Limi- 

 colse. 



With reference to secondary myological points, there are four 

 which, in my estimation, deserve special attention. They are : — 



1. The presence or absence of the expansor secundariorum muscle. 



2. The presence or absence of a special muscular slip from the 

 biceps humeri to the patagium. 



3. The area of origin of the obturator internvs. 



4. The degree of development of the tensor-cruris fascice. 

 These will be considered separately. 



1. The presence or absence of the Expansor secundariorum muscle. 



Expansor secundariorum is the name which it is my habit to 

 employ for a very small and peculiar triangular muscle arising 

 from the quills of the last few (generally two or three) secondary 

 * VkleV. Z. S. 1874, p. 116. 



Proc. Zool. Soc— 1876, No. XIII. 13 



