998 
sends a branch across to join its fellow on the 
right side in the splanchnic nerve. This forms 
a ganglionic enlargement on the mesenteric 
artery, and, after communicating with the right 
trunk of the par vagum, terminates on the intes- 
tines and other viscera. On each side of the 
aorta the prolongation of the sympathetic is 
continued down to the tail, giving filaments to 
the lateral branches proceeding from the aorta, 
and communicating with the spinal nerves. 
Near the anus filaments are sent off, which 
unite and accompany the spermatic artery to 
the ovaries. 
According to the united testimony of Costa, 
Rathke, and Goodsir, no vestige of a brain 
or encephalic enlargement of the medulla 
Spinalis 1s visible in Branchiostoma, a fact of 
extreme interest to the physiologist. In these 
extraordinary Fishes, the spinal cord, as de- 
scribed by the last mentioned gentleman, 
stretches along the whole length of the spine, 
is acuminated at both ends, and exhibits not 
the slightest trace of cerebral developement. 
It is most developed in its middle third, where 
it has the form of a riband, the thickness of 
which is about one-fourth or one-fifth of its 
breadth; and along this portion also it pre- 
sents On its upper surface a broad but shallow 
groove. The other two-thirds are not so flat, 
and are not grooved above. They taper off 
gradually, the one towards the anterior, the 
other towards the posterior end of the Fish. 
From fifty-five to sixty nerves pass off from 
each side of the cord; but as the anterior and 
posterior vertebra are very minute and run into 
one another, and as the spinal cord itself almost 
disappears at the two extremities, it is impos- 
sible to ascertain the exact number either of 
vertebre or spinal nerves. These nerves, Mr. 
Goodsir assures us, are not connected to the 
spinal marrow by double roots, but are inserted 
into its edges in the form of simple cords. 
The nerves pass out of the intervertebral for- 
amina of the membranous spinal canal, divide 
into two sets of branches, one set (dorsal 
branches) running up between the dorsal mus- 
cular bundles; the others (ventral branches) 
run obliquely downwards and backwards on 
the surface of the fibrous sheath of the vertebral 
column, and are distributed to the muscles of 
the ventral region. 
When an entire animal is examined by trans- 
mitted light and a sufficient magnifying power, 
the anterior extremity of the spinal cord is ob- 
served, as before mentioned, to terminate in a 
minute filament above the anterior extremity of 
the vertebral column. The first pair of nerves 
is excessively minute, and passes to the parts 
around the mouth. The second pair is consi- 
derably larger; it sends a considerable branch, 
corresponding to the dorsal branches of the 
other nerves, passes upwards and backwards 
along the anterior edge of the first dorsal mus- 
cular bundle. This branch joins the dorsal 
branches of the third and of a considerable 
number of the succeeding pairs of nerves, at 
last becoming too minute to be traced further. 
After sending off this dorsal branch the se- 
cond pair passes downwards and backwards on 
PISCES. 
each edge above the hyoid apparatus, and joins 
all the ventral branches of the other spinal 
nerves in succession, as its dorsal branch did 
along the back. This ventral branch of the 
second pair is very conspicuous and may be 
traced beyond the anus, but is lost sight of 
near the extremity of the tail ; it evidently cor- 
responds with the nerve represented in Sig. 531, 
1, as the dorsal communicating branch does 
with the nerve marked 4 in the same figure. 
Sense of smell.—In the structure of their 
olfactory apparatus Fishes present a remark- 
able difference from all other vertebrate ani- 
mals; their nostrils are in fact quite uncon- 
nected with the respiratory passages, consisti 
of mere sacculi, into which the surroundi 
water obtains free access, which are li 
with a pituitary membrane folded into regular 
plice, so as to offer an extensive surface for 
contact. Their usual situation is towards the 
fore part of the face, where they are supported 
by the vomer, the maxillary, and the intermax- 
illary bones, the first suborbital bounding their 
lower margin, while above they are arched — 
over by a bone distinguished by Cuvier as the 
nasal. 
The openings of the nostrils are of a round, — 
oval, or oblong shape; they are situated either 
at the end of the muzzle or upon its sides, or 
upon its upper surface, or sometimes even 
beneath, as in the Rays and Sharks, where 
they are found near the angles of the mouth. 
In the Lamprey they are placed quite at the ~ 
summit of the head, and open by a common 
orifice; but in the greater number of Fishes, 
perhaps in all the osseous races, each olfactory” 
sacculus presents two orifices, one in front, the: 
other behind, which are sometimes sufficiently 
remote from each other, but both orifices open 
into the same cavity. : 
The anterior orifice sometimes has its € zee 
tubular, as in the Eel, and sometimes this 
tubular edge is prolonged, as in the Lote and 
some of the Siluridz, into a tentacle of more 
or less considerable length: at other times these 
tubular prolongations are wanting, as in the 
Scombride, in which family, moreover, the 
posterior nostrils are but vertical slits. a 
The nostrils of the Lophius ~— me 
able peculiarity, each being suppo upon ; 
little gotta je! as to resemble a mushroom, th 
expansion of the mushroom containing th 
oltactary cavity, which, as usual, communicates 
with the exterior by two little orifices. " 
In some rare instances the posterior apertar 
of the olfactory sacculus is situated bene 
the lip, a circumstance which is more especial 
remarkable in some foreign Congers, and e: 
hibits a remarkable approximation to what 
met with in the amphibious Proteus and Sirei 
The disposition of the pituitary membra 
that lines the nasal sacculus is simp 
where the shape of the olfactory cavity is rot 
the folds of the membrane which lines it are’ 
posed like the radii of acircle (fig. 529); bu 
the nasal fosse are oblong or elon 
are arranged along the two sides of ana 
very regular folds, resembling in their arre 
ment the barbs of a feather. In the nun 
