724 THE ANATOMY OF THE RUFFED GROUSE 



The quadrate bone consists of three processes. The otic process has one condyle, as in most 

 ])iimitive birds, and articulates with the squamosal, thus forming the main articulation of 

 the jaw. The orbital process protrudes into the posterior region of the orbit. The ventral 

 process is divided into two parts, one of which articulates with the lower jaw and the quad- 

 rato-jugal arch, while the other is more medial and articulates with the pterygoid. 



The external aspect of the lower jaw is formed from the dentar\ . angular and surangular. 

 The dentary forms the most anterior part and extends posteriorly to the fenestra between the 

 surangular and the angular, and on the lower edge passes beyond the fenestra for some dis- 

 tance. The surangular meets the quadrate. From it there are two processes: the internal ar- 

 ticular process extends into the orbit for a little distance: the retroarticular process curves 

 upward around the posterior part of the quadrate. The latter is a long process on which is 

 inserted M. depressor mandibulae. On the internal aspect of the jaw, the splenial bone is 

 discernible, covering the inner side as far posteriorly as the fenestra. The other elements 

 of the lower jaw are completely fused to the angular and surangular. 



In general, the skull of Bnnasa is much lighter than tliat of nther members nf the Tetraoni- 

 dae. The skull of Lagopiis is proportionallv shorter, broader and higher, andr' has no slit 

 between the nasals and the nasal process of the premaxilla. Centrocercus has a highly arched 

 bill and low frontal region. The nasals are as in Lagopus. The prevomer ossifies, although 

 it is verv small. The mandibular fenestra is slit-like. Tyinpaiiuchiis has a large prefrontal 

 bone, a long postorbital process and the prevomer is ossified. 



Vertebral Column. There are fifteen separate cervical vertebrae, including the atlas and 

 the axis. The atlas, which bears the head liv means of a socket into which fits the occipital 

 condyle, is a ring-shaped bone possessing poslzygapophvses and an articulation on its lower 

 posterior surface for the odontoid process of the axis, upon which the whole revoKes. The 

 postzygapophyses of the axis form a wide flange of bone. The next two vertebrae have this 

 flange of bone ])enetrated by a fenestra, as in Galliis. The following six vertebrae are elon- 

 gated and have the renniant of a rib fused to the diapophysis and directed posteriorly. Their 

 postzygapophyses are long and thin, bearing their articular facets at tiic tip. The next {\\f 

 vertebrae are shorter and stouter. The second I axis I. third and fourth vertebrae each pos- 

 sess a sharp, keel-like hv|)a|>o])h\sis. On the fifth, the li\ pa|)ii|)h\sis is a small narrow process. 

 In these characters Boiiasa differs from Galliis in «lii(li tlii> hypapophyses are long and 

 sharp"'". The last four cervicals each have an anteriorh direiled hvpa|)o])hvsis. but the sixth 

 to eleventh vertebrae imhisive lack hypapophyses. The terminal ccr\ ical \ertelira possesses a 

 comparativeI\ short, thin, cervical lib which is articulated willi imili ilic rcniiurn and the dia- 

 ])ophvsis but which does not reach the sternum. The traiisM-rse foianieii is progressively 

 larger till, in the last cervical vertebra, it is lacking. 



There are five thoracic vcrteiirac of wiiirli the first four arc fll^ed. DorsalK. there is a 

 ridge formed from their fused neural spines. The tips of the first three hypapophyses are 

 fused, thus forming two fenestrac on the ventral side. The tip of the middle hyjiapophysis 

 is ex|)anded to form a small plate, as in Tympanuchus. In Callus, the first fenestra is 

 smaller. The tips of the transverse processes are idimcclcd and the foramina thus formed are 

 partK filled by a thin film of bone. The articulation for the head of the rib is clearly visible 

 on the last three thoracic vertebrae. The free lliora<ic vcilclira has long transverse proces.ses 

 and an arli( nlai facet for the M'xcntll rili. 



Posterior of lln' sacrum lii' the five free caudal vertebrae and the loosely atlaihed terminal 

 pygoslylc which is sharpK pointed and protrudes slighlh upward. F.ach vertebra has a trans- 



