heart gives off posteriorly a second
median vessel which divides almost at once into a right and a left
half, each of which again divides into two vessels which run to the
dorsal and ventral mantles respectively. The dorsal branch sends a
blind twig into each of the diverticula of the dorsal mantle-sinus,
the ventral branch supplies the nephridia and neighbouring parts
before reaching the ventral lobe of the mantle. Both dorsal and
ventral branches supply the generative organs.

The blood is a coagulable fluid. Whether it contains corpuscles is not
yet determined, but if so they must be few in number. It is a
remarkable fact that in _Discinisca_, although the vessels to the
lophophore are arranged as in other Brachiopods, no trace of a heart
or of the posterior vessels has as yet been discovered.

_Muscles._--The number and position of the muscles differ materially
in the two great divisions into which the Brachiopoda have been
grouped, and to some extent also in the different genera of which each
division is composed. Unfortunately almost every anatomist who has
written on the muscles of the Brachiopoda has proposed different names
for each muscle, and the confusion thence arising is much to be
regretted. In the Testicardines, of which the genus _Terebratula_ may
be taken as an example, five or six pairs of muscles are stated by A.
Hancock, Gratiolet and others to be connected with the opening and
closing of the valves, or with their attachment to or movements upon
the peduncle. First of all, the adductors or occlusors consist of two
muscles, which, bifurcating near the centre of the shell cavity,
produce a large quadruple impression on the internal surface of the
small valve (fig. 13, a, a'), and a single divided one towards the
centre of the large or ventral valve (fig. 12, a). The function of
this pair of muscles is the closing of the valves. Two other pairs
have been termed _divaricators_ by Hancock, or _cardinal muscles_
("muscles diducteurs" of Gratiolet), and have for function the opening
of the valves. The divaricators proper are stated by Hancock to arise
from the ventral valve, one on each side, a little in advance of and
close to the adductors, and after rapidly diminishing in size become
attached to the cardinal process, a space or prominence between the
sockets in the dorsal valve. The _accessory divaricators_ are,
according to the s