The anatomy of Ijucapina crenulata. 



463 



The buccal sinus is a great cavity beneath the mouth and pharynx 

 in which lie the radular supports. The muscles attached to the latter 

 are freely bathed in the arterial blood. The radular sheath (Bad. t) 

 also connects with the buccal sinus on the right posterior side. In 

 this way the newly forming end of the radula is constantly supplied 

 with the purest blood. There are four arteries leaving the buccal 

 sinus from its posterior floor. A pair of moderately large openings 

 to the pedal arteries, situated one on each side, and two rather small 

 openings close together almost equally distant from each of the first 

 two. The median smaller pair {N. a) lead into vessels surrounding 

 the great pleuro- pedal nerve 

 trunks, which will be spoken of 

 later. These vessels are really 

 the neural arteries, correspond- 

 ing to the arteries surrounding 

 the pedal nerve cords in Hali- 

 otis, where they run the whole 

 length of the animal. In Luca- 

 pina however, the pedal cords 

 being very greatly concentrated, 

 the neural arteries are short and 

 lie on the surface of the foot. 

 They are not broken up into 

 capillaries before entering the 

 venous circulation, but inosculate 

 freely with the veins covering 

 the floor of the visceral cavity. 

 The pedal arteries (Fig. L P. a) 

 springing from the outer open- 

 ings, go at once into the muscular 

 tissue of the foot. Each artery 

 goes to the posterior end of the 

 animal , giving ofl" capillaries 

 along its whole length. 



All parts of the foot receive 

 arterial blood from this source, 

 some of the capillaries coming so 

 close to the ventral surface that 

 they often break out during injection. From the anterior end of each pedal 

 artery a small branch is given off (L.p. a), which runs posteriorly and 



Fig. L. Circulation of the foot, the ven- 

 tral surface has been removed showing the 

 pedal arteries, P. a, and one of the mai'ginal 

 pedal arteries, L.p. a. 



