150 Transactions. — Zoology. 



Hinge and articular cartilages (pi. 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 ; hut the outline is in most parts irregular. 



A thin cartilaginous plate of oval outline lies at the base of the 

 funnel. 



Muscles. 



On a dissection along the posterior surface being made, one of the most 

 striking features are the musculi retractores infuiylibuli (pi. iv. a) extending 

 from the base of the 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 oesophagus, with the mass of the 

 liver. 



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 (pi. 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 



