(_b_) At the _posterior end_ of the cranium the most prominent feature is the large, almost circular =foramen magnum=, through which the spinal cord and brain communicate; this in young birds is seen to be bounded by four distinct bones, dorsally by the =supra-occipital=, ventrally by the =basi-occipital=, and laterally by the =exoccipitals=. 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 middle line by a pair of holes, the =anterior openings of the Eustachian canals=; while just in front of these and a little further removed from the middle line are the anterior openings of the =carotid canals=. Bristles passed in through the posterior openings of the carotid canals will emerge here (fig. 60, A, 27). In front of the basitemporal the base of the cranium is formed by the =rostrum= (fig. 60, A, 31), or thickened basal portion of the interorbital septum; this bears two prominent surfaces with which the pterygoids articulate. In some kinds of duck these surfaces are borne by well-marked basi-pterygoid processes.