THE CEPHALOPODA 299 
inner base of the crown of arms: one such buccal pouch occurs in 
Loligo and two in Sepia, and they may play an accessory part in 
fecundation. In some exotic species of Sepia there are pouches in 
the mantle. 
II. ANATOMY. 
1. Lhe Alimentary Canal.—The digestive tube of Cephalopoda 
comprises a buccal mass with two mandibles and a radula, a long 
oesophagus, a muscular stomach with a pyloric caecum, and a short 
intestine which turns forward and opens in the middle line below 
the funnel (Fig. 252, a). 
The buccal aperture, situated in the middle of the pedal 
appendages et 260, oa is surrounded by a circular lip garnished 
with papillae. °F urther- 
more, in the decapodous 
Dibranchia there is a 
buccal membrane which 
may be very extensive 
Fic. 266. 
7 YBA 
ee Eze Mandibles of Nautilus, 
Minute structure of the cartilage of Loligo. in situ, dorsal aspect. 
a, simple, and b, dividing cells; ¢, canaliculi; d, im, lower or ventral 
an empty cartilage capsule, with its pores; e, mandible ; w.m, upper or 
caualiculi in section. (From Lankester, after dorsal mandible. (After 
Furbringer.) Owen.) 
and be divided into lobes alternating with the arms,'and the lobes 
may even be furnished with small suckers, as may be seen in some 
species of Loligo. 
The buccal cavity or pharynx has very thick muscular walls. 
Internally it is provided with two powerful mandibles, one ventral 
and the other dorsal (Fig. 266); the tip of the ventral mandible 
overhangs that of the dorsal, forming a beak like that of a parrot 
(Fig. 268, vm, dm). These mandibles have recurved insertion-plates, 
to which the large muscles forming the greater part of the mass of the 
buccal bulb are attached. In Nautilus the trenchant borders of the 
mandibles are covered by a calcareous deposit (Fig. 266), and the 
fossils known by the name of /t/yncholiths are nothing else than 
the beaks of Tetrabranchia ; for instance, Rhyncholithes hirundo is the 
beak of Temnocheilus bidorsatus, of the Trias. 
