162 MR. R. OWEN ON THE ANATOMY OF THE BRACHIOPODA. 
h’. hk’. Fig. 16. The insertions of these muscles into the opposite valve. 
i.i. The posterior pair of muscles of the perforate valve. 
k. k. The fringed brachia, or labial arms. 
l.l. Their free spiral extremities. 
m.m. The branchial vessels ramifying upon the mantle-lobes. 
n. The two systemic hearts. 
o. The mouth. 
p. The stomach. 
q. The liver. 
r. The ova. 
PLATE XXIII. 
Anatomy of Orbicula. 
Fig. 1. Orbicula Cumingii, Brod., natural size. 
1*. Orbicula strigata, Brod. 
2. Group of Orbicula lamellosa, Brod., natural size. 
3. External surface of the lower or flattened valve of Orbicula lamellosa. 
4. Internal surface of the same. 
a. a. The muscular impressions. 
b. The fissure through which the pedicle passes. 
c. The central process, or ridge of the perforated valve. 
5. The soft parts of Orbicula lamellosa, in situ, after the removal of the convex 
valve ; showing the ciliated and vascular mantle, the shell-muscles and 
visceral mass. 
6. The soft parts of Orbicula lamellosa, exposed by the removal of the flattened 
and perforated valve, showing a similarly organized mantle-lobe, and the 
expanded base of the pedicle, or foot. 
7. The soft parts, as in Fig. 5, farther exposed by reflecting the mantle-lobe. 
The stomach and decussating visceral muscles are shown by the removal 
of the liver and ovary. 
8. The soft parts, as in Fig. 6, similarly exposed by the reflection of the mantle- 
lobe, and the removal of the liver and ovary. The whole course of the 
intestinal canal is here seen. 
9. The visceral mass and reflected portions of the arms, with their spiral ex- 
tremities, and the cavities in the muscular stem exposed. The alimentary 
canal, with the mouth and anus, and the liver and ovary, are shown. 
10. A side view of the soft parts, with the mantle-lobes separated to show the 
anus just below the bend ef the right arm, the spiral extremity of which 
is unfolded. 
