A^o. 2.1 SHUFELDT ON NORTH AMERICAN TETRAONID^. 319 



Those interesting osseous and diminutive oblong plates, the sclerotalsy 

 present in so many of the class, are found here occupying their usual posi- 

 tion. (Plate V, Fig. 51, 2, and Plate X, Fig. 75, in Oupidonia.) They num- 

 ber from thirteen to eighteen or twenty, and their function is so well 

 known that it will not be dilated upon here. They differ principally in 

 the amount of tenacity with which they retain their normal relation, after 

 prolonged maceration. Cupidonia holds a high place here, and the fact 

 seems to be due to the greater overlapping of the edges of these little 

 affairs and the toughness, or perchance the thickness, of the internal and 

 external sclerotic coats that cover them. Lately w^e saw in the case of 

 Sayornis nigricans where these platelets were apparently confluent ; no 

 such condition ever occurs in the Grouse or Partridges. 



The "lacrymal" (Plate V, Fig. 51, 3 and other figured skulls) is 

 found on the anterior margin of the frontal, enjoying a free harmonial 

 articulation that encroaches slightly on the nasal border. Each is a 

 squamous, cordate lamella, with its larger end nearer the orbital cavity ; 

 this completes the bone in young birds, but in mature individuals it 

 sends down a curved and delicate style with its point directed outwards, 

 that encircles and gives support to the lacrymal duct on its passage to 

 the rhinal cavity {Centrocercus). 



We now come to examine into the last of the cranial vertebrae, and, 

 in the family under consideration, the one most modified. It is the 

 " nasal," and its neural arch the " rhinencephalic," the haemal, the 

 " maxillary." 



In the Tetraonidce its centrum, the " vomer," is missing. We make 

 this assertion boldly, for, after careful scrutiny in the embryo, we find 

 no special ossification for that segment, nor can we appropriate hon- 

 estly any part of the pre-sphenoid to compensate for the deficiency, and 

 we are the more convinced of the fact after examining crania of birds of 

 different ages. It is absent. Whether this be due to the foreshortened 

 skull of the Grouse, with its long sphenoidal rostrum rendering any fur- 

 ther extension superfluous, we cannot say. In the lengthened skull of 

 any of the Anatidoe, where such a bone is imperatively called for, as a 

 sub-interspinal partition, it is invariably present, and unusually jiromi- 

 nent (Plate V, Fig. 51, rr. vomer, is merely outlined to indicate its 

 position in other birds). 



The neurapophyses of the arch are found in the connate prefrontals, 

 the bone called ''ethmoid" in androtomy. It here, in the young- 

 bird, is lodged in the outer third of the groove on the pre-sphenoid, rises 

 columnar, sub-compressed laterally, leaning forwards at a gentle angle 

 to expand above in a trihedral summit for the suj)iiort of the frontals, 

 nasals, and intermaxillary, a short process being projected backwards 

 for the former. The posterior aspect of the column develops as the bird 

 grows, the iuterorbital septum, reaching to, and perhaps aiding in, the 

 formation of the exogenous orbito-sphenoids. 



The nasals, or tlie divided neural spine of the arch, are squamous 



