SKELETON OF THE WILD DUCK. THE SKULL. 315 



The basi-occipital forms the main part of a prominent 

 convex knob, the occipital condyle, with which the atlas 

 articulates. The occipital condyle is slightly notched above, 

 and the ventral surface of the cranium is deeply pitted just 

 in front of it ; the exoccipitals also contribute slightly to its 

 formation. Slightly in front of and ventral to the foramen 

 magnum is a small foramen through which the hypoglossal 

 nerve leaves the cranial cavity. 



The supra-occipital is separated from the parietal by a 

 suture line along which run a pair of prominent ridges, the 

 lambdoidal crests (fig. 60, B, 30). There are often a pair of 

 prominent vacuities in the supra-occipital dorsal to the foramen 

 magnum. The epi-otics and opisthotics become completely 

 fused with the bones of the occipital segment at a very early 

 stage. 



(c) The ventral surface of the cranium is wide behind, 

 where it is formed by a broad ' transverse membrane bone, the 

 basitemporal (fig. 60, A, 23), the sides of which are fused with 

 the auditory capsules. Slightly in front of and an eighth of 

 an inch external to the hypoglossal foramen the cranial wall is 

 pierced by a pair of foramina through which the tenth or 

 pneumogastric nerves leave (fig. 60, A, X). At the sides 

 of the basitemporal are a pair of depressions, the tympanic 

 recesses, in each of which are three holes. Straight lines 

 joining these holes would form an isosceles triangle with its 

 apex directed forwards. Of the two holes at the base of the 

 triangle, the one nearer the middle line and leading into the 

 cranial cavity, is for the exit of the ninth or glossopharyngeal 

 nerve (fig. 60, A, IX), it lies just in front of the pneumogastric 

 foramen. The more external leads into the tympanic cavity, 

 while the more anterior at the apex of the triangle is the 

 posterior opening of the carotid canal (fig. 60, A, 25), 

 which traverses the base of the cranium, and during life 

 lodges the carotid artery. 



The anterior end of the basitemporal is pierced near the 



