150 Transactions.— Zoology. 
Hinge and articular cartilages (pl. iv., b, c).—The hinge cartilages are two 
developments, one on each side of the funnel. Part of the cartilage is free 
and expands slightly on the surface, having a longitudinal central groove. 
The portion that is imbedded in the substance of the funnel is triangular in 
section, the base being at the surface. This cartilage is long and narrow, 
and the ends of the surface-portion are rounded. 
Corresponding with these hinge cartilages are two slightly raised car- 
tilaginous ridges, one on each side of the inner posterior surface of the 
mantle. These cartilages are not so marked as those of S. brevis, Owen 
(Trans. Zool. Soc. of Lond., vol. xi., pt. v.). When the mantle is contracted 
they fit into the cartilaginous sockets on the funnel. They extend quite to 
the mantle-border, forming the angles that on the posterior surface give the 
appearance of shoulders. It is impossible to observe any definite outline in 
the imbedded portion; indeed it would seem that the ridges are rather 
hardened elevations of the mantle than true cartilages. 
Pinnal cartilages.—A long cartilage, having a low thickened central 
ridge with thin dilatations on each side, extends the whole length of each 
fin. A section in the thickest part shows a low triangle, whose broad base 
lies against the body of the animal, and to whose sides the muscles of the 
fins are attached; but the outline is in most parts irregular. 
A thin cartilaginous plate of oval outline lies at the base of the 
funnel. 3 
Muscles. 
On a dissection along the posterior surface being made, one of the most 
striking features are the musculi retractores infundibuli (pl. iv. a) extending 
from the base of thè funnel to somewhat beyond the centre of the anterior 
surface of the mantle, where they are attached, one on each side of the 
gladius. In the groove between these elongated muscular masses lie the 
intestine and ink-sac, the penis and the œsophagus, with the mass of the 
ver. 
The double muscular band already spoken of as being attached to the 
neck cartilage probably serves to change the position of the neck. The 
neck has also two well-marked muscular masses lying under the musculi 
retractores infundibuli. 
Each arm shows a central mass of muscle-fibres channelled for blood- 
vessels and nerves. From this central mass radiating fibres are given off 
to a circular muscular coat lying beneath the surface of the arm. 
Gladius (pl. viii., fig. 1). 
The gladius is lanceolate in shape, and is transparent. The central rib 
is well marked, and has a deeply excavated channel. It extends beyond 
the dilated wings about one-sixth of the total length. The broadest part is 
