258 NEW YORK STATE MUSEUM 



tion is developed on the outer aspect of this part of the bone; that 

 above apparently takes the place of part of the coronoid process. 



Each mandibular facet presents two oblique grooves upon an area 

 contracted to the minimum surface for the accommodation of the 

 mandibular foot of the quadrate that articulates with it. 



Behind, either angle is produced backward as a recurved and 

 vertical lamina of bone, to the inner side of which we find the 

 circular entrance to a deep conical pocket. In all essential par- 

 ticulars the lower jaw of the Hooded merganser agrees with these 

 characters as found in the Red-breasted species we have under 

 consideration. 



Mergus serrator has an enormous bilobed tracheal tym- 

 panum at the pulmonic bifurcation of its windpipe. These in- 

 teresting structures vary much in form and size in the different 

 species of birds that possess them, and would well repay a general 

 comparison. 



Vertebral column and ribs. This merganser has 61 vertebrae 

 in its spinal column, the first pair of free ribs occurring on the 

 1 6th; then follow five others that have ribs connecting with the 

 sternum by costal ribs; 17 anchylose to form a sacrum for the 

 pelvic bones ; and, finally, we find seven free caudal vertebrae 

 besides a pygo style. All these segments are freely movable upon 

 one another, except those in the sacrum. In Mergus the odon- 

 toid process of the second vertebra does not perforate the cup of 

 the atlas from behind, but both these segments, in common with 

 many ducks, present the interesting condition of having the lateral 

 vertebral canals at the outer sides of their centra, for the protection 

 of the vessels that pass through them. This canal is a very prom- 

 inent feature through all of these cervical vertebrae to include the 

 1 2th; in the first five or six it has a fenestra in its lateral wall on 

 either side. With the exception of the last few vertebrae in which 

 it occurs, it extends nearly the full length of the centra, while its 

 inferior wall includes the greater part of the parial parapophyses, 

 and these latter being rather widely separated, we have as a result 

 a broad area at the under side of all of these vertebrae where this 

 condition obtains. 



The hyapophysial canal is found in the 6th to the 12th, inclu- 

 sive, but in none of these does it close in entirely, though the pro- 

 cesses approach each other very near in the last mentioned vertebra. 



Axis vertebra has a prominent hyapophysis, but it is missing in 

 the 3d vertebra, and this process does not make its appearance 



