THE SKELETON OF THE VERTEBRATE HEAD. 14Y 



the post-frontal process, and may have a branch of communi- 

 cation with the antero-inferior projection of the mastoid, as in 

 certain parrots. It may also extend down to the malar, and 

 may be connected in this direction with the transverse pro- 

 jection of the so-called " ethmoid," or pre-sphenoidal centrum. 

 The infra-ocular bony arch in the maccaws and certain other 

 birds is not a zygornatic arch, although consisting like it of 

 actinapophyseal elements. The proper zygomatic arch, as 

 consisting of the malar and squamosal, exists in all birds ; 

 the infra-ocular arch is ossified in comparatively few. 



The reference of the lachrymal and the other bony forma- 

 tions round the orbit in birds to a muco-dermal system by 

 the continental anatomists and by Professor Owen, appears to 

 me to be disproved by their relation to the soft parts. They 

 are all developed in aponeurotic bands, which enter into the 

 formation of the orbital fascia already alluded to. In a band 

 extending along the margin of the sphenoido-frontal, the 

 supra-orbital bone takes its rise, which may thus become con- 

 nected with the lachrymal, when that bone, which is developed 

 in the anterior extremity of the band, extends backwards in it. 

 A second band extends downwards and backwards from the 

 lachrymal to the malar, forming a ligament between the two 

 bones, and along which ossification may extend. A third 

 band extends from the post-frontal process downwards and 

 forwards to the quadrate-jugal or squamosal, along which 

 ossification may extend from above. In all birds a band 

 connects the lachrymo-malar with the post-fronto-squamosal 

 band, thus forming an arch below the under eyelid. The ex- 

 tension of ossification into this commissural band, probably 

 from both extremities, completes the infra-orbital bony arch, 

 and may approximate or unite it to the squamoso-jugal or 

 proper zygomatic arch. A fibrous band, which extends down- 

 wards and forwards in the temporal fascia from the anterior 

 process of the mastoid, becomes ossified in some birds ; and 



