853 
ZOOLOGY. 
ticular processes of certain bones of the cranium. In the 
one-horned rhinoceros they adhere to a rough, and slightly 
elevated surface of the vast nasal bone. The front horn of 
the two-horned species has a similar attachment; the pos¬ 
terior rests on the os frontis ; as those of the horned pecora 
do. Two kinds of structure are observed in the latter : there 
are either proper horns, as in the genera of the ox, goaf, and 
antelope, or bony productions, as in the genus cervus, which 
includes animals of the deer kind. See the articles Bos and 
Cervus. 
We have not supplied any plates of the skeleton and mus¬ 
cular system of the mammalia, several very fine plates being 
already in the body of the work. See, for example, Far¬ 
riery. 
In treating of the nervous system, we shall commence 
with an account of its anatomy, without any reference to its 
functions, and shall conclude with some speculations as to its 
physiology. For the first part, we shall content ourselves 
with a condensation of what is said by Carus and Desmou¬ 
lins. 
As to th e form of the nervous system, the first point to be 
noticed is, that the appearance which it first assumes is a circle 
around the oesophagus, which constitutes its most unitorm 
and fundamental portion. The farther development of this 
fundamental type appears to correspond to the diversity of 
the general organization, and, in accordance with it, to take 
one of three d.rections. In tire first, the nervous ring receives 
considerable additions to its bulk by the formation of larger 
ganglia in its substance, which gradually approximate more 
and more to each other on the superior side of the animal, 
the situation most peculiarly assigned to the nervous mass; 
such is the case in the mollusca. Secondly, in the articu¬ 
lated worms, &c., the jointed form of the body is accompa¬ 
nied by a multiplication of the nervous rings surrounding 
the alimentary canal; and the ganglia of these generally im¬ 
perfect rings being connected together in a continued chain 
on the abdominal surface: or, thirdly, in insects, the deve¬ 
lopment of the nervous system takes place in both the pre¬ 
ceding ways, i. c., capitally and longitudinally. 
51. A, the undersurface of an asterias, the rays being cut 
away: a, nervous circle around the mouth; b, the smaller; 
c, central larger nervous branches to the rays of the body; 
B, lobes of the liver from a ray of the asterias rubus; C, 
cluster-shaped ovary from the same. 
In the fresh-water muscle (mya pictorum) it is always easy 
to distinguish the nervous system, after the animal has been 
macerated a few days in spirit of wine. Here, also, we find a 
nervous ring loosely surrounding the short cesophagus, with 
two ganglia of considerable size on each side; these send two 
long fibres backwards over the gills, which combine to form 
a large ganglion in that situation. The fourth and most con¬ 
siderable ganglion, however, first described by Mangili, is 
seated in the substance of the foot, beneath the ovary, being 
the lowest ganglion of the nervous ring on the abdominal 
surface; the superior one corresponding to the brain in the 
higher classes of animals being deficient. 
In the figures 36 and 37 we have representations of 
the brain and senses in the snail: in fig 36, the horns are 
marked 1, 2, 3, 4; their muscles a a and bb; cc de¬ 
note the muscles retracting the lips; and the brain, d, is 
composed of two spherical lobes, placed on the anterior 
part of the head when the animal is moving, but which 
can be retracted by muscles along with the mouth g, 
stomach h, salivary vessels i i, into the interior of the 
animal. We shall describe it as it exists in the fore part of 
the head. The optic nerves arise from the front of these 
globes, and make many spiral turns, n, before they arrive at 
the extremity of the larger horns, a disposition evidently for 
the purpose of allowing the retraction and advancement of 
the brain; 11 indicate slender ligaments which defend the 
nerve; m and o, a muscle which moves its envelope. The 
nerve terminates by a swelling at p, which is finally sur¬ 
mounted by the eye, q: r indicates the nerves which go to 
the extremities of the smaller horns; they are contorted like the 
optic, but differ from them in the two circumstances, that 
Vol. XXIV. No. 1677. 
they are not surmounted by eyes, nor arise directly from the 
brain. They arise from two nerves, s, that supply the roots 
of the smaller horns. The roots of the larger horns are sup¬ 
plied by nerves marked t; u indicates the muscles which 
move the throat and mouth, whiclrare also represented at h in 
fig. 37, where we may perceive how they become folded 
when the brain is advanctd. 
In fig. 37, a marks the parts of the throat, stomach, and 
palate. The stomach, b, is cut off to shew the brain, c; dd are 
two columns of the spinal chord, which leave an interval be¬ 
tween them for the passage of the stomach; they unite and 
form a ganglion, e, which gives off all the nerves of the 
lower part of the body, viz., nerves of the organs of genera¬ 
tion,;;; of the skin and muscles of these parts, q; of the 
muscles of the sides, rr. A long nerve from the right side 
of the ganglion passes, accompanied by a muscle, to the 
ovary, s. Two other nerves arise behind this: one accom¬ 
panies it, the other, t, passes to a transverse muscle, situated 
on the limbus; u marks a similar nerve on the left side, 
which goes to the left and under side of the body; y y y, the 
nerves on the left going to the side; z z, their antagonists on 
the right, cut off. 
At fig 39 is represented the nervous system in a sepia. 
Fig. 55. PI. IV. A leech (hirudo medicinalis), opened 
longitudinally, together with the intestinal canal, from the 
dorsal side: a, the sucking surface of the mouth ; b, the ca¬ 
vity of the mouth opened, with an internal view of its trian¬ 
gular aperture; c, muscles of the pharynx; d, cavity of the 
pharynx; e, the cerebral ganglion above it; f, the perforated 
septum of the stomach; g, the chain of ganglia; h, respira¬ 
tory vesicles; i, the lateral vessel ; k, the pylorus; 1, dilata¬ 
tion at the commencement of the intestine; m, the intestine; 
n, the anus: o, the anal sucking surface; p, the cavity of the 
stomach; q, the coeca; r, the female, s, the male genital 
organ. 
55. PI. V. A portion of the chain of ganglia, from the 
anterior part of the body of the same. 
At fig. 39, we have engraved the nervous system of the 
saepia octopus; a, the brain, composed of two lobes; b, the 
fat that encloses it, and is enclosed by a cartilaginous cup ; 
c, the optic nerves, partly covered with fat; d, ganglia formed 
on them, which give rise to several nerves, e e, which are 
distributed to the eye; f a vessel they enclose; g, fibrils 
that embrace the choroid coat, and perhaps form it; h, a 
spherical enlargement, on which is situated the chrystalline 
lens; i, the fore-part of the brain gives out three pairs of 
nerves, 1, 2, 3, distributed to the head, feet, and adjacent 
parts: on the middle one a ganglion, n, is situated. The 
hinder part of the brain sends off two large nerves, q, which 
pierce the thorax, pass under the muscles that move the two 
concave bodies of the excretory sac, and each forms a gan¬ 
glion, r r, whence many other nerves arise which are distri¬ 
buted to the stigmata. 
The unmarked figure, in Plate V., shews the cartilage of the 
head, cerebral ganglion, &c. of the scepia officinalis; a, the 
cerebral ganglion; b, nervous collar around the cesophagus 
(c); d, optic nerves; e, their ganglia and ramifications;^ 
the eye; g, k, nerves of the viscera and cloak; little au¬ 
ditory sac, with the auditory nerve; i, cavity of the labyrinth 
in the cartilage of the head (/); m, the orbits. 
Fig. 38 represents the nervous system of the louse, in 
which the medulla oblongata is seen as a striated body 
through the skin: a a a, three remarkable swellings in the 
spinal chord, whence arise three nerves, bb b, which go to 
the muscles of the six feet; c c, other nerves that supply the 
viscera. The last swelling of the spinal chord differs little f rom 
the others; it is thickly covered with tracheae. Tile cerebral 
end of the spinal chord is a very thin thread, e; thus differing 
from what is found in other insects, who have this part always 
divided into two and threaded by the cesophagus. The brain, 
ff is of the form of two round pears joined to each other by 
the larger ends. It is studded with tracheae, g g, and fatty 
particles, which render its demonstration difficult on account of 
their close adhesions ; h h are the optic nerves ; i i, the eyes. 
Fig. 40 represents the spinal marrow of a bee: a, the supe- 
9 F rior 
