( 7 ) 
The brain of Birds has the same general characters as that of 
other oviparous vertebrated animals, hut it is distinguished by a 
very considerable proportionate size, which often even surpasses 
that of the same organ in Mammalia. Its volume consists prin- 
cipally of tubercles, analogous to the canneUs,''' and not in the 
hemispheres, which are very thin, and without circumvolutions, (i) 
The cerebellum is tolerably large, almost without lateral lobes, 
and almost entirely formed by the vermiform process. 
The trachea of Birds has its rings entire ; at its bifurcation is a 
glottis, generally provided with distinct muscles, and called the 
inferior larynx; it is there that the voice of birds is formed ; the 
enormous volume of air contained in the aerian cavities contributes 
to the strength, and the trachea^ by its various forms and move- 
ments, to the modifications of the voice. (2) The superior larynx 
is very simple, and does not avail much. 
The face or superior beak of Birds, formed principally by their 
intermaxillaries, is prolonged behind in two arcades ; the internal 
(1) This is the corpus rectiforme^ which makes a part of the cere- 
bellum in Birds ; there is no middle lobe, which disappears in all the 
Mammalia below Apes. Sensibility is considered to depend on the 
proportion of brain and nerve: in our common Ducks and Fowls, the 
brain is not more than 1-30 0th part of the size of the whole body, 
whilst in Swallows, Parrots, Canaries, and others, it amounts to l-14th 
part. Thus, the former, in whom a much smaller proportion of nerve 
is developed, are unequal to the art of making nests; whilst the latter 
display much ingenuity in the fabric, know where to find them again 
after a long absence, whistle and sing in their dreams, and displa}- their 
superior sensibility in a variety of ways. We know that Swallows fre- 
quently fall to the ground in fits from their extreme sensibility. 
(2) See fig. 13, wherein^ is \h.e glottis, which is of a horny sub- 
stance. In Mammalia the bifurcation takes place without the inter- 
vention of a glottis. The inferior larynx is enlarged variously (some- 
times into two large lobes) according to the nature of the voice of the 
bird. The circles which are continued all round in Birds^ extend only 
half round the tracheae of Mammalia. In the latter the voice is 
formed in the upper part of the trachea ; in the former, in the lower or 
distinct part of which we have been speaking, and which has a small 
apparatus within, precisely similar to the mouth of a clarionet ; whilst 
in Mammalia the trachea contains two chords only, which vibrate 
whenever we choose to pass a current of air through them, and thus 
produce the voice. This may be demonstrated in a degree by blowing 
gently through the tracheae of Mammalia and Birds ^ even after dis- 
section. Referring to this, M. Cuvier, in his Comparative Anatomy, 
has happily compared the trachea of Birds to u wind, and that of Mam- 
malia to a stringed instrument. 
