FUNNEL AND CAPITO-PEDAL CARTILAGE. 763 



in connection with the anterior pallial artery may be observed. It will be remembered 

 that upon approaching the mantle border in the mid-ventral line, this artery bifurcates 

 into two submarginal arteries (vi.p.a.). 



The submarginal pallial artery is continued dorsally on each side into a branch of 

 the systemic or greater aorta, so that a complete arterial circuit, the circulus pallialis, 

 is achieved. I have even partially injected the pallial arteries from the dorsal aorta 

 itself, although naturally the fluid did not proceed very far in the centripetal direction. 

 Thus by means of the submarginal arteries the system of the lesser aorta becomes 

 confluent with that of the greater aorta, or in other words, there is an anastomosis 

 between the pallial circulation and the systemic circulation. 



In one of the figures here reproduced the union of the submarginal arteries with 

 the dorsal aorta is represented as seen through the mantle ; in the other it is shown 

 after the mantle has been slit open and turned back, and a further incision made into 

 the body-wall in the nuchal region. The vessel which effects the junction is called 

 the pallio-nuchal artery (p.n.a.). The actual point where the confluence takes place 

 corresponds with the umbilical region of the mantle, and with the angle of insertion 

 of the mantle in this region into the body-wall. 



From the angles formed by the confluence of the pallio-nuchal with the submarginal 

 arteries a branch is distributed forwards to the nuchal membrane. (Fig. 7.) 



Finally I have to record some observations in the pallial veins. Under ordinary 

 circumstances one might never suspect the occurrence of definite venous channels in 

 the mantle. When a Nautilus kept in a confined space becomes moribund, it usually 

 rises to the surface, owing apparently to an abundant production of gas in the interior of 

 the body. If it be allowed to die and be then removed from the shell the veins are 

 found to be injected with gas, most likely due to a regurgitation of gas, if the expression 

 may be allowed, through the siphuncular venous sinus and posterior pallial vein, into 

 the general venous or lacunar system of the body. Under these conditions the finest 

 ramifications of the veins, especially in the free mantle-flap, are displayed with a clearness 

 which could hardly be attained, certainly not surpassed by artificial injection. The mantle 

 in fact is seen to be riddled by these veins, which are collected into two main channels, 

 placed on either side of the anterior pallial artery, and discharging behind into the 

 afferent branchial vessels. At the sides of the mantle there may be seen a number of 

 lateral pallial veins, which appear to open into a large sinus situated over the shell 

 muscle. (PL LXXXII.) 



8. Funnel and Capito-pedal Cartilage. 



It is a fact of some interest which deserves to be brought into relief, that the 

 cartilaginous endoskeleton of Nautilus essentially belongs to the funnel, it is the 

 sustentaculum infundibuli besides serving incidentally as the foundation and support of 

 the entire cephalopodium, and affording a fulcrum for the insertion of all the principal 

 muscles of the body. It agrees analogically in point of form with the hyoid cartilage 

 of Vertebrates and the nuchal chondroid skeleton of Enteropneusta, consisting as it does 



w. vi. 100 



