HAG-FISHES. 
1 201 
proper, but only with the above-mentioned cartilaginous 
rods, situated in its foremost part. The six gill-sacs 
(br) on each side communicate inwards by means of a 
short transverse duct with the oesophagus; outwards 
each of them emits a longer duct (hr), curving down- 
wards and outwards. These latter ducts coalesce on 
each side into a single canal, thus finding an orifice 
on the two outer sides of the body at an opening 
situated far back, the two outer branchial apertures 
(fig. 358, s; fig. 363, k). 
Nervous system. The brain of Myxine exhibits a 
rudimentary structure with decidedly retrogressive cha- 
racters (figs. 357 and 359). As mentioned above, the 
investing cerebral capsule consists of cartilage under- 
Fig. 358. Branchial apparatus, heart, branchial artery, and oesophagus 
of Myxine glutinosa, after Johannes Muller. Nat. size. 
o, oesophagus; i, inner branchial ducts; hr , gill-sacs; br\ outer bran- 
chial ducts, which coalesce and have a common opening at s, the outer 
branchial aperture; a, atrium of the heart; v, its ventricle; ab, branchial 
artery, which sends a division to each sac; d, flaps of skin, folded back. 
neath alone; its sides and roof are of a fibrous texture. 
The brain is first enveloped in a thin, blood-vascular, 
connective tissue, a kind of pi a mater , which descends 
into and fills the cerebral sulci. Seen from above (fig. 
359) the naked brain is triangular, with the base of 
the triangle directed forwards. By a dorsal longitu- 
dinal sulcus in the median line a bisection into two 
lateral halves is indicated. In each lateral half five 
divisions, bounded by transverse sulci, may be traced, 
namely, beginning from in front, the olfactory brain, 
forebrain , midbrain, hindbrain, and afterbrain. Of the 
' tweenbrain there appears dorsally, in the angle between 
the forebrain and midbrain, a small, rounded or oval 
protuberance, the ganglion habenulae, usually consisting 
of a right and a left lobe; but of the epiphysis itself 
not a trace can else be detected; on the ventral side 
is a small infundibulum with a lamellar appendage, 
the hypophysis. The afterbrain (medulla oblongata) is 
strongly developed; its anteriorly dilated central canal 
advances through the midbrain to a ciecal termination, 
somewhat before the posterior half thereof. The third 
ventricle is obliterated, with the exception of two small 
vestiges. Of lateral ventricles there is no trace. No 
ependymal pallium, like that of the Teleosts and Petro- 
9 
Fig. 359. Brain of Myxine glutinosa, seen from above, X 7. 
a, olfactory lobe; b, forebrain; c, midbrain; d, hindbrain; e, after- 
brain; f, ganglion habenula;; g, spinal cord; h , nasal duct with carti- 
laginous rings; i , olfactory organ with cartilaginous basket; k , eye; 
l, optic nerve; m, trigeminus; n, facialis (?); o, trigeminus (?); p, 
acoustic nerve ; q, vagus ; r, sensor}- roots of spinal nerves. 
myzon larvte, is to be found. It is hence impossible 
for the present to determine with certainty in the adult 
state whether the forebrain of Myxine merely corre- 
sponds to the corpora striata, or whether the cerebral 
pallium also enters into its structure. 
The nerves issuing from the brain on each side 
are: olfactorius, opticus, trigeminus, facialis, acusticus, 
and vagus', of the others no trace can be seen. 
