294. M. Krokn on the Anatomy and 
round the base of the hooks outside and behind, im proceeding 
toward the lower surface of the head, behind the mouth. As we 
have already said, the hood only covers a portion of the head, 
leaving the lower surface almost completely exposed ; the result 
is, that its lateral parts must be wider than its upper and lower 
portions. Between the two leaflets composing it we observe very 
evident slender fascicles of fibres, which have a parallel course to 
the outline ; these fibres probably serve for the expansion of this 
part, whilst a simple mechanical action, the straightening of the 
hooks, and the swelling of the head, which is the consequence of 
it, casts back this organ. 
Hooks.—These are composed of horny fibres, excessively de- 
licate, and having a longitudinal direction. Their base is hollow, 
and contains a substance which becomes white and turbid in 
spirits of wine; it is probably a kind of bulb destined to rege- 
nerate the hook when this latter is worn or destroyed. 
Muscular apparatus.—The principal mass of the head is com- 
posed of muscles arranged symmetrically on the two sides of 
the head; the most voluminous among them are those which 
form its base, and on this account, these masses, seen in profile, 
appear to be ‘obliquely truncated ; im fact, each of them consti- 
tutes the corresponding half of ‘the head. When they are in 
action, raising the hooks, they form two considerable emmences 
which project beyond the two prominences which surround the 
mouth. They are resolved into numerous fascicles, the direction 
of which it is difficult to detect. We know however positively 
that most of these fascicles are inserted at the base of the hooks, 
and others on to a thin and hard plate, which I must here de- 
scribe. This plate exists on each side, immediately beneath the 
skin. It extends on the surface of the muscles in question, at 
first between the bases of the hooks and the points of insertion 
of the hood; it then forms a curve, following this insertion as far 
as the anterior margin of the head ; and lastly, growing thinner, 
enters into the eminences which bear the lttle spmes above- 
mentioned. 
With regard to the other pairs of muscles, I confess that I 
have not been able to follow them m a satisfactory manner ; 
their minuteness baffled my patience ; and if I were able to indi- 
cate the origin and insertion of some of them, I should still find 
it impossible to explain their action. 
Pharynx.—The pharynx is a short duct, situated m the mid- 
dle of the head, and only a little wider than the stomachal swell- 
ing. Liaterally, it is limited by the two muscles of the hooks, 
and, as it seems also, by walls furnished with very decided mus- 
cular fibres, crossing one another. 
II. Trunk.—The cavity of the trunk is filled, durmg the life 
