622 
thomboidal sinus: this may be seen in the 
goose. The medulla oblongata, with the py- 
ramidal and cerebellic fasciculi, present similar 
characters to the same parts in the fishes; the 
corpora olivaria, and pons Varolii, are not yet 
developed. 
The brain of birds is composed of a similar 
number of as in the reptiles, but they are 
more highly developed, and they are no longer 
arran in a longitudinal series as formerly, 
but more on the top of each other. In the 
sea-gull (Larus cyanorhynchus, fig. 355), 
— (Scolopax gallinula), red start ( Mota- 
ci ?), goldfinch ( Fringilla carduelis ), 
fowl (Phasianus gallus, fig. 356), pigeon 
( Columba ——?), and hawk (Falco nisus ), 
the brain fills entirely the cranial cavity, this 
cavity now corresponding exactly with the size 
and form of the head. It is of increased re- 
lative size compared with the body: in a pi- 
geon, weighing according to Carus 3360 grains, 
the brain weighed 37 grains; the proportions 
being as 100 : 9,100. 
On taking a review of its structure, we find 
three principal portions, as heretofore, to oc- 
cupy our attention, the conformation of each 
being very uniform in the whole class: 1st, the 
cerebral hemispheres ; 2d, the optic lobes; 3d, 
the cerebellum. 
ist. The cerebral hemispheres, or first cere- 
bral mass, are large (figs. 355, 356, a, a), of 
greater relative size than any other parts of the 
brain, and vary but little in form ; in the embryo 
Fig. 355. 
Brain and portion of spinal marrow of Larus cyano- 
th |, about natural size. 
@, @, first cerebral mass or cerebral hemispheres. 
5, b, second cerebral mass or optic lobes. c, third 
cerebral mass or cerebellum, with its transverse 
grooves. d, spinal cord, with its posterior longi- 
tudinal fissure. 
chick on the sixteenth day, however, I found 
them very little larger than the optic lobes 
(fig. 357, a). In the sea-gull and snipe they 
are of an oblong form, and larger posteriorly ; 
in the hawk more round and short; in the 
red-start, goldfinch, pigeon, and embryo chick, 
on the twentieth day, more lengthened in form 
and covering quite the optic lobes (fig. 357, a). 
In the ostrich they are also lengthened and 
pig very much the form and characters 
of the same _— in the lower Mammalia, 
These hemispheres are united to each other by 
a commissure (the anterior commissure); above 
NERVOUS SYSTEM. (Comparative Anatomy.) 
Fig. 356. Fig. 357. 
cord of Pha 
Brain and ion of spinal I 
(fowl), state, age 16 days, slight 
ae ‘st 
stanus 
a, a, first cerebral mass or cerebral hemi: 
of a triangular form. 5, b, second cerebi a 
or optic lobes, touching at their inner borders. , 
third cerebral mass or cerebellum, small. d, sp 
cord, with its posterior longitudinal fissure. 
olfactory nerves. 4 
Fig. 357. The same, age 20 days, slightly 
a, a, first cerebral mass or cerebral hemis; 
oval in form. b, b, second cerebral mass or op 
lobes, widely separated from each other. ¢, thi 
cerebral mass or cerebellum, greatly increased 
developement and pushing asunder the optic lob 
d, spinal cord, with its posterior longitudinal fissu 
g, olfactory nerves. 
this there is another one, which Meckel eo 
siders as the first rudiment of the corpus ¢a 
losum ;* they contain cavities which are tr 
lateral ventricles, and in a a tubercle o 
enlargement corresponding to the corpus st 
eas of the Manmalik From the ante 
part of this primary cerebral mass the olfactor 
nerves arise (figs. 356, 357, g, 8), and pa 
forwards to the cribriform plate of the ethmo 
bone; their origin is marked by two distin 
enlargements, which are hollow and commit 
cate with the lateral ventricle. ’ 
2d. The optic lobes, or second cerebral m 
4 Sig. 355, 6), are of small size, and are more 
widely separated from each other than in 
preceding classes, though they still are 
nected by a medullary membrane corresp 
ing to the roof of the aqueduct of Sy 
In the embryo of the chick on the sixteenth 
however, these parts, as before observed 
nearly as large as the cerebral hemispl 
their inner borders touching each other, 
the reptiles and fishes (fig. 357, 6): at the: 
tieth We they are widely separated (, fig. 3 
In the sea-gull (fig. 355), snipe, hawk, 
start, goldfinch, fowl, and pi they 
a rounded form, and situated immediate 
neath the cerebral hemispheres. On ¢ 
into them in the sea-gull and pigeon, 
found to contain a cavity, which, in the 
is very small, in the latter larger, an 
taining a solitary dark-coloured tu 
their cavities _communicate with the — 
ventricle. Between these optic lob 
immediately inferior to - cerebral 
spheres, in the pigeon, there is situat 
pair of ganglia, ph i flattened form (the 
istence of which has been before noticed it 
a 
* Archiv. fiir Physiologie. : 
