210 COMPARATIVE ANATOMY CHAP. 



in the Oegopsidce ; among these are the arteria genitalis, which runs to the genital 

 glands, and, in the Myopsidce, a fine vessel called the arteria anterior. 



At certain places, the arteries may swell out to form small muscular and con- 

 tractile widenings, called peripheral arterial hearts. 



In the venous system of Sepia, the venous blood in each arm collects (partly 

 through capillaries and partly through lacunae) into a vein running down the inner 

 side of the arm. All the brachial veins convey their blood to a circular cephalic 

 sinus surrounding the buccal mass, which is the reservoir for collecting the venous 

 blood from the whole head region. Out of this sinus springs the large vena 

 cephalica, which runs up along the posterior side of the oesophagus and the liver 

 into the visceral dome, collecting on the way venous blood from the liver, the funnel, 

 etc. A little below the stomach it forks, forming the two venae cavse, which open 

 into the two contractile venous hearts at the bases of the gills. From the upper 

 part of the visceral dome the blood collects into several abdominal veins, the most 

 important of which are an unpaired vena abdominalis, opening into the vena 

 cephalica exactly at the point where it divides into the vense cavse, and two lateral 

 abdominal veins, which open into the latter near their point of entrance into the 

 branchial hearts. 



In the region of the heart, all these veins carry acinose or lobate appendages 

 (venous appendages), which are hollow, and communicate at many points with the 

 veins, so that they are richly supplied with blood. The cavity into which these 

 appendages project is that of the renal sacs, and the epithelium which covers them 

 belongs to the epithelial wall of the kidneys (cf. Fig. 186, p. 224). We thus see 

 that here the blood flowing back from the body has abundant opportunity of giving 

 off its excretory constituents to the kidneys. 



Appendages are found on both the branchial hearts ; these are the pericardial 

 glands, which will be further described later. The two branchial hearts, by their 

 contraction, drive the venous blood into the afferent branchial vessel. The blood, 

 which has become arterial in the gills, flows through the efferent branchial vessel 

 (the so-called branchial veins) into the auricles of the heart, and thence into the 

 ventricle (on the branchial circulation, cf. p. 96). 



In the Cephalopoda, unlike the other Mollusca, the whole of the blood, in 

 returning from the body, flows through the gills, so that the heart contains only 

 arterial blood. By far the greater part of the blood, before entering the gills, conies 

 into contact with the kidneys in the venous appendages. 



In the Octopoda, the venous system shows some not unimportant modifications. 

 In Octopus, two veins, connected with one another by anastomoses, run along the 

 outer side of each arm and collect the venous blood. At the bases of the arms these 

 veins become connected in pairs, and unite later in such a way as to form on each 

 side a lateral cephalic vein. 



These two veins unite to form the large vena cephalica, which runs up in front 

 of the funnel and behind the oesophagus. The brachial veins do not here, as in 

 Sepia, convey their blood first to the venous cephalic circular sinus, but are directly 

 connected with the cephalic vein. A cephalic sinus nevertheless exists in Octopus ; 

 it is not, however, connected with the vena cephalica, but with a large sinus which 

 fills the whole visceral dome, and is, in fact, the primary body cavity, in which 

 the viscera lie bathed by the venous blood. The latter flows out of this large 

 venous sinus through two wide veins, the so -called peritoneal tubes, into the 

 upper part of the vena cephalica, near the point where this divides into the two 

 vense cavse. 



Nautilus is chiefly distinguished by the absence of the branchial hearts. 

 Further, each of the two vense cavae divides into two branches, which run, as 

 afferent vessels, to the gills. 



