OSTEOLOGY OF BIRDS 



59 



The condyle is hemispheroidal in form, and very small ; it barely 

 encroaches upon the periphery of the foramen magnum. This lat- 

 ter aperture is nearly round, and lies quite in the plane of the basi- 

 cranii. This condition seems to be characteristic of the Falconidae. 



A posterior view of the skull of Circus presents a smooth, semi- 

 globular surface. At its lower part, in the median line, we observe 

 a well developed supraoccipital prominence, with a decided con- 

 cavity on either side of it. On this view we are just enabled to see 

 the condyle, and only the outer projections of the quadrates. Later- 

 ally, the squamoexoccipital wings hide other things from view be- 

 yond. Above these wings the sphenotic processes hang down. The 

 shallow median groove passes between the parietal eminences. In 

 the brain case we observe that the carotid openings are separate, 

 being some distance apart in the pituitary space [fig. 23]. 



The wall covering the anterior semicircular canal is much raised, 

 while beyond it the usual group of foramina for the exit of tht 

 seventh (the vagus) trifacial division of the fifth and other nerves 

 are seen. 



The fossae for the lodgment of the several encephalic lobes are 

 very deep, and this condition is hightened by an ossification of the 

 tentorium, which divides them, for some little distance beyond the 

 inner cranial wall along the site of the attachment of that membrane. 

 The optic nerves make their exit at separate openings, already 

 alluded to above. 



The greatest amount of diploic tissue is found between the inner 

 and outer cranial tablets, at the vault of the cavity, or that portion 

 covered by the frontal bones, as it is in these latter that it exists. 

 In the superoccipital region it is quite scanty, and the cranial walls 

 are here very thin [fig. 23]. 



Many of the bones in the skull of this harrier are pneumatic, this 

 part of the skeleton when dried weighing but 38 grains (Troy), and 

 this includes the lower jaw. 



The mandible may be said to partake of the V-shaped variety, and 

 the symphysis is gently curved downward anteriorly so as to look 

 upward and forward. Each ramus has rounded superior and in- 

 ferior borders, and their width is quite uniform from the coronoid 

 process to the symphysis on either side [fig. 19, 24]. 



Upon this aspect, too, we observe that the ramal vacuity, seen in 

 so many birds, indeed in other species (Falco), has here been en- 

 tirely absorbed. Every evidence of original sutural landmarks has 

 been obliterated, and the mandible of Circus is as good an 



