No. 2.] SHUFELDT ON NORTH AMERICAN TETRAONID^. 317 



osseous extension, chiefly from the ethmoid, frontals, and ali-sphenoids, 

 and that the basi-sphenoid sends up on either side two delicate bony- 

 sprouts, that subsequently complete the periphery of the circular foramen 

 for the oculomotorial nerve. This fact has been likewise carefully 

 studied in the cranium of the common barn-yard fowl, and like conclu- 

 sions arrived at. So that in Plate V. Fig. 51, this, as it occurs in some 

 other birds, has been simply outlined and marked os.; in tliis same 

 figure Fr. is the " frontal," ps. the prefrontal or centrum of the 

 vertebra, and co the usual site for the postfrontal — this exogenous ele- 

 ment, the diapophysis of the vertebra is not here found, its position 

 being occui)ied by a depressed roughened surface for the squamous 

 articulation of the mastoid. We have never personally examined anj^ 

 bird in our avi-fauna where this bone is seen independent. Descriptive 

 ornithotomists, in their studies upon the skulls of Rheidce and 

 Struthionidce give the presence of this process as occurring free. 



The neural spine of the frontal vertebra follows the example of the 

 parietal in being completely bifidated in the younger specimens. As a 

 whole it is perhai)S the largest segment in the bird-skull — certainly as 

 far as our Grouse and Partridges are concerned. Either half of its 

 spine presents projecting anteriorly from the middle a flattened pro- 

 cess, directed gently forwards, downwards, and outwards • that at its 

 extremity is marked above by quite an extensive surface for one of the 

 nasals, and below by another, against which the head of the ethmoid 

 abuts. The concave surface below this process and the remaining 

 hinder moiety forms the vault of the orbit. Another scale-like pro- 

 jection is thrown out posteriorly, deeply concave within, correspond- 

 ingly convex without, to shield the prosencephalic lobes — the bones 

 being joined. Huxley terms the pleurapophysis of the hiiemal arch of 

 this segment the "quadrate" — the "os quadratum" of the older anato- 

 mists. Owen defined it as the tympanic, it being the homologue of a 

 bone of the vertebral skull generally — it was the os carr^, in birds, in 

 the writings of the eminent Cuvier. The tympanic forms no exception 

 here in the Tetraonidm to birds of America generally, in being a free 

 bone, of various shapes in divers families a,nd genera. So symmetrical 

 is it found to be in the Grouse, that little harm would be done, were 

 such a step advisable, to appoint it as a type for the Class. The mas- 

 toidal and orbital arms are about of a length and calibre, the first being 

 rather the larger, and is surmounted by a hemispherical articulating 

 head for the cup on the lower border of the mastoid. The neck below 

 the processes is moderately constricted before it expands to become the 

 "mandibular" end, that has beneath, its transverse elliptical facet out- 

 wardly, the intervening notch and then the inner and smaller one, all for 

 articulation with the mandible. The bone has likewise a surface to 

 articulate with the pterygoid below the orbital process, and is always 

 pneumatic. From the outer aspect of the mandibular extremity it sup- 

 ports its two appendages, the bony styles, termed "squamosal" and 



