Four vessels, which, according to the above view, are analogous to bronchial 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 cavity4 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 at ce,ce.) 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 The branchial vein (f) receives the aerated blood from vessels extending along the convex margins of the respiratory laminm, 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 (g) 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.
Two arteries arise from it ; one superior and small (h), 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 (/). 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 pallial 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 cesophagus, 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, fig. 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 stern of the branchia, by the vein marked/.
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, li)e the venous follicles of the Nautilus above described.
In no species of Cephalopod vvhich has hi therto been anatomized, have these appendages* been found wanting ; but they vary in form in different genera. In the Genus Eledonet they form thin colourless pyriform sacs, extending nearly an inch from the vein. They are ar ranged in distinct clusters, and are relatively shorter in Argonauta. In Sepioteuthis the whole extent of the superior and inferior trunks of the veins contained in the pericardium pre sent an uniform and continuous cellular en largement of their parietes. In Loligo the coats of the corresponding veins in like man ner present only a spongy thickening. In Sepia the cells are more elongated, but are large, irregular, and flocculent (c, c, fig. 225), and continued without interruption not only upon the divisions of the vena cava (a), but upon the visceral veins, two of which ( b,b) present remarkable dilatations.