168 MEMOIRS OF THE CARNEGIE MUSEUM 



"By the kindness of Mr. R. C. McGregor and Mr. Curtis Clay Young the Museum 

 some time ago came into the possession of an extremely good series of Cormorant 

 skulls of all ages, and by means of these it is possible to trace the process of ossifica- 

 tion very well. These seem to show that the desmognathism of the Cormorant's 

 skull is caused by the growth of bone between the maxillaries, and is not due to any 

 outgrowth of those bones themselves." 



" This ossification commences between the backward processes here considered as 

 the maxillo-palatines and progresses until they are firmly united. The union of the 

 anterior portion of the maxillaries occurs later and is due to the extension of ossifi- 

 cation into the tough lining of the roof of the mouth, and there is frequently a small 

 space between the maxillaries which remains open for a long time if not perma- 

 nently" (Fig. 13). 



"The formation of the fronto-nasal hinge (Fig. 14) is a secondary character, the 

 bones so overlapping in young birds that there is no freedom of movement in this 

 region." 



"The absence of external narial openings is also a secondary character, for the 

 young Cormorant possesses perfectly open nostrils while the cranium is almost as 

 schizo-rhinal as that of a gull (Fig. 15). As growth proceeds the narial openings 

 become more and more restricted, until about the time (the exact time is uncertain) 

 that the young birds take to the water, not only the external openings, but those of 

 the cranium have become completely filled." 



Passing once more to the skull in the adult we find the interorbital septum is 

 unossified, as is the greater part of the anterior wall of the brain cavity. However, 

 we here find the "foramen rotundum" separated from the far larger vacuity above, 

 by a transverse bony bar. A subcircular vacuity also occurs in the mesethmoidal 

 plate ; and the sphenoidal rostrum is not as large as the zygoma. 



Phalacrocorax urile differs from the Anhinga inasmuch as in it the pars plana does 

 not ossify ; and in the form of its lacry mal bone. One of these in this Cormorant is seen 

 to be fused with the frontal bone and nasal above; is laterally composed; not in con- 

 tact with the maxillary below, where it sends outwards a short process, and inwards 

 a longer and slenderer one, the mesial end of which fuses with the mesethmoid (see 

 Fig. 12). 



This specimen (No. 18982, Coll. U. S. Nat. Mus.) lacks a vomer, and it was not to 

 be found in my skeleton of Anhinga; in the latter, if it ever existed, it may have 

 been lost but I see in another place, where remarking upon the osteology of P. 

 bicristatus (now urile) (Science, N. Y., v. 11, No. 41, Nov. 16, 1883, p. 640), I have 

 said that in it "we observe a long attenuated vomer, terminating anteriorly in a free 



