722 THE ANATOMY OF THE RUFFED GROUSE 



the difFerent bones can be identified. 



The posterior aspect of the skull is sub-circular. The foramen magnum, bounded by the 

 occipital bones, is round except on the ventral border where the occipital condyle protrudes. 

 On each side of the foramen are two small foramina for the hypoglossal nerve. The glosso- 

 phyaryngeal, vagus and accessory nerves pass out through a more lateral foramen on each 

 side. At the lower lateral margin of the posterior aspect lies the otic region formed by the 

 coalescence of the three otic bones. Just at the edge of this area is a fossa into which passes 

 the internal carotid artery and from which pass out the vena capita lateralis and the palatine 

 branch of the facial nerve. 



TTie orbit occupies most of the lateral aspect of the skull. Anteriorly, it is bounded by 

 the prefrontal (lacrimal) which is a scale-like bone extending from the frontal — to which, 

 however, it is not ankylosed — part way to the jugal arch. The interorbital septum has a 

 small centrally placed fenestra. The posterior wall of the orbit is formed largely by the or- 

 bitosphenoid and the pleurosphenoid ("alisphenoid"), and is bounded by the postorbital pro- 

 cess of the frontal. This process is fused distally with the zygomatic process of the squamosal 

 bone to produce a sharply pointed forward extension which is serrate on its ventral border. 

 The temporal muscles pass through the canal formed by the partial fusing of these two pro- 

 cesses. The squamosal, comprising much of the lateral wall of the brain case as well as a 

 portion of the orbit, is fused anteriorly to the pleurosphenoid, dorsally to the frontal, dorso- 

 posteriorly to the parietals, and posteriorly to the exoccipitals. There is an otic process 

 of the squamosal which protrudes over the otic region. The olfactory tract lies along the 

 underside of the roof of the orbit and has a large opening into the brain case. The optic 

 foramen, through which passes the optic nerve, is large. The oculomotor, trochlear, the pro- 

 fundus branch of the trigeminal, and the abducens ner\'es pass out through separate foramina. 

 In the pleurosphenoid and below the zygomatic process is the foramen ovale for the maxillary 

 and mandibular branches of the trigeminal nerve. 



The otic region lies within a deep fossa, its posterior border being formed by the parotic 

 process of the exoccipital and its anterior border bv the pleurosphenoid. Tlie anterior part 

 of the fossa is a reticulum through which the Eustachian tube passes downward from the in- 

 ternal ear to the mouth. Tti the sidewall of this tympanic cavity is the fenestra ovale, an 

 obvious opening in which lie^ the columella. Tlie facial nerve docs not come out on to the 

 surface of the skull but. with the vena capita lateralis. j)asses through a bony canal just supe- 

 rior to the fenestra ovale. This canal opens to the exterior just medial to the position of the 

 internal carotid artery in the fossa on the posterior aspect of the skull. The semi-circular 

 canals arc not imbedded in solid bone but lie in a spongework. Air enters this area through 

 the Eustachian tube and reaches the parietals and other skull bones through pneumatic 

 openings. 



The j)alate is perfectly schizognathous. The pterygoid extends from the quadrate to the 

 rostrum of the parasphenoid. where it articulates with the palatine. This latter bone, on each 

 side, extends anteriorly, wide at first, and then narrowing to join the palatal processes of 

 the premaxilla, while its posterior external angle is completely rounded off. Tlie maxillo- 

 palatines pass dorsad of the jialatine and are directed ])osteriorly and medially. The rostrum 

 of the parasphenoid is thick and strong. The i)revomcr ("vomer") consists of a pair of carti- 

 lagenous slivers just anterior to the rostrum. The basijitcrygoid processes are represented by 

 two facets on the paras])henoid rostrum. Tli<' paras|)heiioid has two ])airs of openings in its 

 anterior part. The medial pair is for the Eustachian tubes and the more lateral ones for tin- 

 internal carotid arteries. Tlic basis crnnii is roniuh'd and bulcring. 



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