310 STRUCTURE AND CLASSIFICATION OF BIRDS 



The second pectoral is inserted, in an unusual way, on to 

 the anterior face of the humerus, and not on to the pectoral 

 ridge, as in other birds. 



In the hind limb nearly all pigeons have the complete 

 formula ABXY, the ainbiens being sometimes present and 

 sometimes absent. Only in Lopliolcemus apparently is the 

 accessory femoro-caudal absent. 



The deep flexor tendons are gallinaceous, either blending 

 or with a vinculum. In Lopliolamus au- 

 tarcticus and Enjtliroenas there is a vinculum, 

 and also a special slip to tendon of digit II. 



Considering the variability of so many 

 muscles and organs among the Columba3, it 

 is remarkable to note what slight variations 

 there are in that, as a rule, rather variable 

 organ, the syrinx. The accompanying illus- 

 tration will serve to show the form of the 

 syrinx among the Columba3 ; but in the 

 species illustrated the origin of the sterno- 

 tracheales is not so hi 8 hl y asymmetrical as 



latrans (AFTEK i s sometimes the case ; they occasionally 

 arise more markedly from the right side of the 

 trachea. The intrinsic muscles are always present, and 

 generally attached, as shown in the figure, to the membrane 

 between the penultimate and antepenultimate tracheal rings. 

 They are sometimes continued a little further by ligamentous 

 tissue. The last three tracheal rings are united by median 

 bony or cartilaginous pieces. Posteriorly the tracheal rings 

 are weak, or even defective in the middle line. These are 

 the general characters of the windpipe and syrinx in the 

 Colmnbae. A few of the genera which show some slight 

 divergencies may now be mentioned. In Calcenas nicobarica 

 the intrinsic muscles are continued by ligament as far as the 

 penultimate tracheal ring ; the first four or five bronchial 

 semi-rings are connected posteriorly by a cartilaginous bar, 

 which borders the membrana tympaniformis and is continued 

 up as far as the sixth tracheal ring from the end of the 

 series. 



