CEPHALOPODA. 



539 



might flow into the peritoneal cavity, or the 

 fluid contents of that cavity be absorbed into 

 the vein.* 



In the structure of the other veins of the 

 Nautilus nothing uncommon is observed : 

 their principal termination is in the sinus 

 above-mentioned, where the greater or systemic 

 circulation ceases, if we are to consider the 

 lesser circulation to commence where the blood 

 again begins to move from trunks to branches. 



Four vessels, which, according to the above 

 view, are analogous to branchial arteries, (c, c,) 

 arise from the sides of the sinus, and proceed, 

 two on each side, to their respective gills. In 

 this course they have each appended to them 

 three clusters of short, pyriform, closely aggre- 

 gated, glandular follicles (d, d). The larger 

 cluster is situated on one side of the vessel, 

 and the two smaller on the opposite. Each of 

 these clusters is contained in a membranous 

 receptacle communicating with the pericar- 

 dium, and formed by partitions projecting from 

 its inner surface. In these partitions we ob- 

 served a fibrous texture, which conveyed an 

 impression that they were for the purpose of 

 compressing the follicles and of discharging 

 such fluids as might exude through their pa- 

 rietes into the pericardium, whence it might be 

 expelled by the papilliform apertures at the 

 base of the gills into the branchial cavity .f 

 The follicles, however, terminate by their pro- 

 per apertures in the interior of the dilated parts 

 of the vessels to which they are appended : 

 (these are shewn on the right side atd',d'.) We 

 shall revert to these singular bodies in the de- 

 scription of the circulating organs of the Di- 

 branchiata. 



The branchial arteries having reached the 

 roots of the gills become contracted in size, 

 and their area is here occupied by a valve which 

 opposes the retrogression of the blood. Each 

 vessel, then, penetrates the fleshy stem of the 

 branchia (e), where it dilates into a wide 

 canal, which presents a double series of orifices 

 through which the blood is driven by the 

 contraction of the surrounding muscular sub- 

 stance, into the vessels which extend along the 

 concave margins of the branchial laminae. 



The branchial vein (f) receives the aerated 

 blood from vessels extending along the convex 

 margins of the respiratory laminae, by a series 

 of alternate slits, and is continued down the 

 anterior or inner side of the gill. After quit- 

 ting the roots of the gills each vein crosses its 

 corresponding artery on the dorsal aspect, and 

 is continued, without forming a dilatation or 

 sinus, to the systemic ventricle, where regurgi- 

 tation is prevented by a single semilunar valve 

 at the termination of each vein. 



The ventricle (p) is of a somewhat com- 

 pressed and transverse quadrate form : its mus- 

 cular parietes are nearly a line in thickness, 

 and present internally a decussated structure. 



* For a further description of this structure, its 

 analogies, and probable uses, see ' Memoir on the 

 Pearly Nautilus,' p. 27 et seq. 



t We found the pericardium in the specimen 

 dissected filled with coagulated matter accurately 

 moulded to the different parts which contained it. 



Two arteries arise from it ; one superior and 

 small (h) y whose orifice is furnished with a 

 double valve ; the other inferior and of large 

 size (i), coming off from near the left angle of 

 the ventricle, and furnished with a muscular 

 bulb about five lines long, at the termination 

 of which there is a single valve ; and which 

 ought rather to be considered as a continuation 

 of the ventricle. The lesser aorta gives off a 

 branch to the great gland of the oviduct; a 

 second, which is continued down the membra- 

 nous siphuncle of the shell ; and a third to the 

 fold of intestine (I). The larger aorta passes 

 downwards between the gizzard and ovary, and 

 renders vessels to both these viscera. It then 

 winds round the bottom of the pailial sac, sends 

 off large branches to the liver, and gains the dorsal 

 aspect of the crop, along which it is continued, 

 distributing branches on either side to the 

 great shell-muscles, to the cephalic cartilage, 

 where it divides into two equal branches, 

 which pass round the sides of the oesophagus, 

 and furnish branches to the mouth, the sur- 

 rounding parts of the head and the funnel. 



In the Dibranchiata the veins of each arm 

 form two principal branches, which descend 

 along the lateral and posterior parts of those 

 appendages; each lateral vein unites at the base 

 of the arm with the opposite vein of the adjoin- 

 ing arm ; the united vessel is joined by another 

 similarly formed ; and the whole of the venous 

 blood is thus ultimately conveyed to an irre- 

 gular circular sinus, from the anterior part of 

 which, between the head and the funnel, the 

 great anterior cava is continued. In the Octo- 

 pus this vessel (a, Jig. 226) is provided with 

 two semilunar valves, where it communicates 

 with the venous circle. A little below this 

 part it receives the veins of the funnel ; then 

 those of the anterior part of the liver ( b) and 

 of its muscular envelope. Upon its entrance 

 into the pericardium the vena cava divides 

 without forming a sinus as in the Nautilus ; 

 and sometimes before, sometimes after its divi- 

 sion it is joined by two large visceral veins 

 (c). Thus reinforced, each of the divisions 

 (d, d) proceeds downwards and outwards to 

 the lateral or branchial heart of its correspond- 

 ing side; but previous to opening into the 

 ventricle it dilates into a sinus (e), which also 

 receives the venous blood from the sides of the 

 mantle and the fleshy and vascular stem of the 

 branchia, by the vein marked f. 



Both the divisions of the vena cava and the two 

 visceral veins, after having entered the pericar- 

 diac or venous cavity, are furnished with clusters 

 of spongy cellular bodies (g, g), which open 

 into the veins by conspicuous foramina, like the 

 venous follicles of the Nautilus above described. 



In no species of Cephalopod which has hi- 

 therto been anatomized, have these appendages* 

 been found wanting ; but they vary in form in 

 different genera. In the Genus Eledone-\- they 



* From a consideration of the different particu- 

 lars given in Aristotle's anatomical description of 

 the Cephalopods, Kbhler supposes the part which 

 he calls /uy'rif, mytis, to have been the glandular 

 appendages of the veins above described. 



t Carus, Vergleich. Zootomie, tab. iv. fig. viii. 

 x, Eledone Moschata. 



2 N 2 



