HANCOCK OX THE ANATOMY OF DIBHANCII I A 1 i: CEPHALOPODA. 477 



head. So far as I have yet examined the evnera Lolirjo and Sepia, it 

 appears thai the abdominal portion of the great blool simn is really 



wauling, as is asserted by this di.-t ingiiis'ird I'ivim-Ii :i i i.-i t < »i i i i.-^t ; but in 

 Qnvmastrephe* todarits this is bo! the rase, the middle portion ( .f i!p' 

 sinus still existing in a -modified form. The posterior division lias 

 certainly disappeared, and with it the two posterior venous trunks 

 which pass from it to the vena' cava 1 . The anterior venous trunk o\ 

 however, present, and passes forward 1 > \ the side of the aorla, and 

 with il aseends until it reaches the dorsal surface of t lie liver, exact ly 

 as it does in the Octopodidce. The two vessels then run along \'>>v a 

 short distance by the side of the oesophagus, when the venous irunk 

 suddenly expands, and, enclosing that tube within it, forms for it a 

 Wide sheath. In tins state, with the aorta imbedded in the wall of 

 the sheath, the oesophagus and vein reach the salivary glands, when 

 the vein or sheath again expands, and forms a pouch for the reception 

 of these organs. The oesophageal sinus thus formed, and carrying 

 within it the oesophagus, salivary ducts, and buccal branches of 

 the aorta, passes through the nervous collar, and becomes conti- 

 nuous, in the usual way, with the anterior or buccal division of the 

 sinus. 



Here, then, we have a modified visceral sinus ; and so modified, 

 that its true nature is patent enough. In the first place, it cannot 

 be doubted that this is the homologue of the so-called visceral 

 chamber in the Octopodidce ; or, rather, of what has been termed the 

 oesophageal or median division of it. It contains the same organs, is 

 situated in the same position, and communicates in like manner with 

 the anterior or buccal division of the sinus and with the left vena 

 cava. I have just said it contains the same organs. The aorta, how- 

 ever, might be supposed to be an exception to this; but as it lies 

 apparently in the wall of the sinus, and not merely attached to it, it 

 may be considered to rest virtually within the sinus, — the wall of the 

 sinus itself, as in the Octopodidce, being reflected over it. 



This modified visceral sinus lies packed in a rather loose areolar 

 tissue, but can be easily isolated ; so that no doubt can exist as to 

 the fact, that its wall is really an expansion of that of the venous 

 trunk, which commuuicates with the vena cava. And thus we arrive 

 at the conclusion that the so-called visceral chamber in the Octo- 

 podidce is a veritable venous sinus, with its own proper wall. 



As this so-called abdominal or visceral cavity is the only hiatus in 

 the vascular system, pointed out by Milne Edwards, we might perhaps 

 assume, since we see that this is really a venous expansion, that in 

 these animals we have a completely closed blood system, with proper 

 walls throughout. There is one point, however, which appears still 

 to require elucidation before we can linally adopt this conclusion. 

 The existence of capillaries has not yet perhaps been sulliciently de- 

 monstrated. Milne Edwards apparent ly believes in their presence ; 

 but he has not described them, neither arc his figures satisfactory on 

 this point. And! am sorry that I cannot myself speak to the fact with 



