44 DR. R. W. SHUFELDT ON THE [Jail. 18, 



glancing at the drawings made of them, and which illustrate this 

 paper. 



When Forbes was with us and produced his admirable work upon 

 the anatomy of the Tubinares which were collected during the voyage 

 of H.M.S. " Challenger " ^ he found a great deal that was not only 

 unique in the structure of Petrels, but in forms more or less nearly 

 related to them. And I am of the opinion that when we come to 

 examine carefully into the morphology of Arctic water-fowl, and more 

 especially into that of their " soft parts," we shall discover much of 

 interest, to say nothing of its importance as throwing light upon tlie 

 organization of the types in question, as bearing upon the anatomy 

 of the earlier forms of birds ; for it is among these groups, as we 

 know, that we find many of the more lowly members of the class in 

 ])oint of structure and organization. 



This fact was never more forcibly brought to my mind than after 

 reading Forbes's investigations and observing the points I am now 

 about to describe. 



In S. antiquus (fig. 1, p. 45) 1 find the lower larynx rather broad, 

 and somewhat compressed from before backwards. The semirings of 

 the bronchial tubes seem to be only partly formed in bone, while the 

 last tracheal ring and the pessulus are completely ossified, the latter 

 bar being V-shaped on the vertical section, with the apex above. 

 "What appears to me as most remarkable about this larynx is the 

 mass of fat that overlies it in front, and extends on to its posterior 

 aspect, where it becomes thinner. This fat completely covers the 

 tracheo-laterales muscles, which are inserted on cither side into the 

 middle points of the last tracheal ring. The sterno-tracheales are 

 very large and lie embedded in this mass of fat. These are the only 

 tracheal muscles present. 



Referring to B. marmoratus, fig. 2, we find the structure of the 

 parts to be quite different. In the specimen before me, at least, 

 there is an entire absence of fat from this part of the lower larynx. 

 The anterior extremities of the lower tracheal ring, which is 

 here, too, thoroughly ossified, do not meet so completely as they 

 do in S. antiquus, or perhaps, more correctly speaking, this ring is 

 roundly notched in front. B. marmoratus has a pessulus of a form 

 corresponding very closely to the one described above for S. antiquus, 

 but the tracheal tube above it is rather more cyclindrical, and not so 

 much compressed from before backwards. The lateral tracheal 

 muscles seem to agree quite closely in these two Auks, both as regards 

 their size and points of insertion into the mid-lateral parts of the 

 last tracheal ring, where they dilate slightly as they become inserted. 

 Some considerable difference, however, is to be noted in the sterno- 

 tracheal muscles of B. marmoratus, as will be seen in the figure ; they 

 are given off much higher up on the trachea iu this Auk, and are far 

 slenderer than they are in S. antiquus. 



Unfortunately I neglected to examine the condition of the carotids 



in these two Auks before removing the viscera, as I was intent upon 



not injuring their very brittle skeletons, which had become much 



softened by soaking so long in the partially dissolved fat that encased 



^ W. A. Forbes, Zool. Chall. Exp. vol. iv. pt. xi. p. 1. 



