15. The Morphology of the Ostrich Chondrocranium

S ummary The main points of interset which have emerged from the study of the ostrich chondrocranium are:–  Confirmation of de Beer's account of the formation of an olfactory canal by the apposition of the anterior orbital cartilages to the nasal septum and backwardly directed parietotectals.  Confirmation of de Beer's account of the formation of a pila antotica spuria, separating V 1 from V 2, as a secondary backward extension of the original normal pila antotica.  There is only a very short infrapolar process in the ostrich; the lateral carotid foramen is formed by the extreme flexure of the polar-trabecular against the parachordal region and the fusion of the two regions below the carotid artery.  The origin of the metotic process rudiment in the ostrich throws no light on the nature of this process. De Beer's suggestion that it represents a number of fused cranial ribs is neither confirmed nor refuted, since the earliest mesenchyme is attached both to the otic capsule and to the occipital region.  The columella auris has a low backwardly directed suprastapedial and the chorda tympani takes a pre-columella course; the origin of the nerve is as a normal post-trematic branch of the hyomandibular nerve. This condition is compared with that in other birds.  On general considerations, it is shown that the ostrich chondrocranium conforms closely to the typical avian chondrocranium, with very few indications of a primitive nature.