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 newrapophysial 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 hemal arch of the frontal vertebra has been transferred backwards to 
the parietal one; its plewrapophysis (28), 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 ycung ostrich 
and many other birds traces of the composite character of the hemapophysis 
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 hemal 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 hemal 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 hemapophysis (21) at the other end, and they also support the constant 
element of the diverging appendage of the arch, no. 2. The hemapo- 
physis (21) resumes in birds more of its normal proportions and elongated 
slender form: but the hemal 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 hzemal 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 s: 
the second or hemapophysial ray of the diverging appendage is deve- 
loped in all birds, as in the squamate saurians ; combining the movements 
