8 JOURNAL OF SCIENCE. 



character, and true wings, I.e. fore limbs in which the hand has 

 only three digits, the distal carpals are fused with the metacarpals, 

 and the air-resisting surface is furnished by regularly arranged 

 feathers. 



It still remains to say something about the structure of the skull, 

 which in certain respects is quite unique, presenting characters met 

 with in no other bird. 



In the skull of any bird except the Kiwi we notice three chief 

 regions ; the rounded brain case behind, the narrow pointed beak in 

 front, and between these the orbital region consisting of the two 

 immense eye-sockets separated from one another by a vertical plate 

 of bone called the inter-orbital septum. This corresponds to the 

 bone of the mammalian skull known as the pre-sphenoid, and its 

 peculiar character in the bird is due to the enormously developed 

 eyes encroaching upon surrounding parts and squeezing the inter- 

 vening portion of the skull into a flat plate. In the hinder portion of 

 the beak are contained thin scroll-like bones, the turbinals, very much 

 smaller than the corresponding bones in the skull of a mammal and 

 lying altogether in front of the eyes. In the entire head they are 

 covered by delicate mucous membrane to which the olfactory nerve is 

 distributed and therefore constitute the organ of smell. Lastly the 

 external nostrils are situated at a considerable distance from the 

 pointed end of the beak. 



In the Kiwi Wo striking changes have taken place simulta- 

 neously. The eyes, undergoing a gradual diminution in size, have 

 retreated from the median plane, a considerable space being left 

 between them and the presphenoid. At the same time the tui'binals 

 have enlarged immensely, and, extending backwards, have filled 

 up the space between the presphenoid and the eyes, actually 

 reaching as far back as the posterior boundary of the latter. 

 Thus the skull of Apteryx differs from that of all other birds, firstly 

 in the small size of the orbits, and secondly in having those cavities 

 separated from one another not by a thin inter-orbital septum, but 

 by a spongy mass of bone formed by the posterior portion of the 

 turbinals. 



The turbinals are as complete as those of a dog, and are divisible 

 into two regions, a hinder olfactory region covered by a delicate single 

 layer of epithelium and supplied by the olfactory nerve, and an 

 anterior respiratory region covered by a many-layered horny 

 epithelium and supplied by the fifth nerve. Up to the middle of 

 incubation the whole of the respiratory region of the nasal chamber 

 is filled up by a solid mass of epithelial cells so that there is no 

 passage to the exterior by the nostrils. 



In early embryos the form of the head and the position of the 

 nostrils is normal, but soon after an undoubted bird-form is assumed 

 the nostrils are found to have their final position at the end of the 

 beak. By this time the turbinals are already large but do not extend 

 so far back as in the adult. 



