296 report — 1846. 



visceral system, which are feebly and transitorily manifested in the embryo 

 bird. These spurious cornua project freely or are freely suspended, and are 

 the subjects of singular and excessive development, as has been exemplified 

 in the chapter on Special Homology. 



The bones (10) of the third neural arch protect a smaller proportion of the 

 prosencephalon than in the crocodile, but maintain their neurapophysial rela- 

 tion to it and to the optic nerves: the neural spines (11) cover a larger proportion 

 of the hemispheres, and, with their homotypes (7), exhibit a marked increase 

 of development in conformity with that of the cerebral centres protected by 

 their respective arches. The parapophysis of the frontal vertebra (12) is 

 relatively smaller in the bird than in the cold-blooded vertebrates, and is 

 rarely ossified from an independent centre ; but I have seen this in the emeu, 

 and it appears to have been constantly an autogenous element in the dinornis. 

 The haemal arch of the frontal vertebra has been transferred backwards to 

 the parietal one ; its pleur apophysis (2s), which is simple, as in the crocodile, 

 articulating exclusively with the parietal parapophysis (s), though this in 

 some birds unites with that of the frontal vertebra. In the young ostrich 

 and many other birds traces of the composite character of the hcemapophysis 

 are long extant ; and bear obviously a homological relation to the teleologi- 

 cally compound character of the element in the crocodile : for the pieces, 

 nos. 29, 29', 30' and 31 ultimately, and in most birds early, coalesce 

 with each other and with the hcemal spine (32), the halves of which are con- 

 fluent at the symphysis. 



The centrum (13) of the nasal vertebra is always single, and, when it does 

 not remain distinct, coalesces with the neurapophyses, 14, and pleurapophyses, 

 20, of its own segment, and sometimes, also, with the rostral production of the 

 frontal centrum (9) : it is elongated and pointed at its free termination, and 

 deeply grooved above where it receives the above-named rostrum ; indicating 

 by both its form and position that it owes its existence, as bone, to the ossi- 

 fication of the outer capsule of the anterior end of the notochord. In the 

 ostrich the long presphenoidal rostrum intervenes between the vomer (13) 

 and prefrontals (14). These latter bones manifest, however, as has been 

 shown in the paragraph on their special homology (p. 214), all the essential 

 neurapophysial relations to the rhinencephalon and olfactory nerves : but 

 they early coalesce together, or are connate, as in the tailless batrachians. 

 The neural spine (15) is divided along the middle line ; but in most birds the 

 suture becomes obliterated and the spine coalesces with its neurapophyses, 

 with the frontal spine and with those parts of the haemal arch of the nasal 

 vertebra with which it comes in contact. 



The pleurapophyses (fig. 23, 20) of this inverted arch retain their typical 

 connections with the nasal centrum and neurapophyses at one end, and with 

 the haemapophysis (21) at the other end, and they also support the constant 

 element of the diverging appendage of the arch, no. 24. The hamiapo- 

 physis (21) resumes in birds more of its normal proportions and elongated 

 slender form: but the hamml spine (22) is largely developed though undi- 

 vided, and sends upwards and backwards from the part corresponding to the 

 symphysis of the spine, when this element is divided, a long pointed process 

 (22'), which joins and usually coalesces with the neural spine (15) and divides 

 the anterior outlet of the haemal canal into two apertures called the nostrils. 

 The modification of the inferior arch of the nasal vertebra in the lizard tribe 

 is here repeated. The pleurapophysial appendage, 24, connects the palato- 

 maxillary arch with 2s, and in the ostrich and a few other birds, also with 5 : 

 the second or haemapophysial ray of the diverging appendage is deve- 

 loped in all birds, as in the squamate saurians ; combining the movements 



