PERISTOMIAL HAEMOCOEL ; SYSTEMIC AORTA; CEPHALIC ARTERIES. 781 



side, when a forest of slender conjunctive trabeculae are found passing from the inner 

 (mesial) surface of the liver to the wall of the crop. 



The peristomial haemocoel is virtually separated from the peri-oesophageal space by 

 a tendinous diaphragm on the dorsal side, and by the tissues and organs of the fundus 

 elsewhere. The diaphragm is a very definite structure stretching from the cerebral 

 capsule to the body- wall in the region of the nuchal membrane (PI. LXXXI. fig. 7, and 

 PL LXXXIII. fig. 26). 



The nerve-collar which strictly surrounds the oesophagus is the cerebro-visceral loop. 

 The pedal commissure is separated from contiguity with the oesophagus by an interval 

 which is occupied by the ventral retractor muscles of the buccal mass. The oesophagus 

 passes into the buccal mass precisely at the level of the fundus of the peristomial 

 haemocoel, so that the oesophagus proper lies entirely within the peri-oesophageal haemocoel, 

 the buccal mass 1 with its attendant muscles and nerves being the only portion of the 

 digestive apparatus which occurs within the limits of the peristomial haemocoel. 



The cerebral portion of the cerebro-visceral nerve-collar lies within the peristomial 

 haemocoel (PL LXXXI. fig. 7) while the vis- 

 ceral portion lies within the peri-oesophageal 

 haemocoel (PL LXXXIII. fig. 26). Within 

 the mass of the cephalopodium at the angle 

 of junction of the cerebral and visceral por- 

 tions of the nerve-collar occur the cephalic 

 organs of special sense (eye, rhinophore, and 

 otocyst) and their nerves. The demarcation 

 of these components of the nervous system is 

 therefore clear. 



The greater or systemic aorta of Nautilus 

 arises as a large truncus arteriosus 2 from the 

 left dorso-posterior region of the heart and 

 leaves the pericardium through the left peri- 

 cardio-visceral fontanelle. On its mesial side 

 as it leaves the heart it is adherent to the 

 ligament which binds the heart to the floor 

 of the pericardium. Haller (1895) points out 

 that this cardiac ligament is a very primitive 

 structure, representing the place of origin of 

 the heart in the coelom. 



Having emerged from the pericardium, 

 the great aorta, after a short upwardly directed 

 course through the perivisceral coelom, enters the peri-hepatic haemocoel between the 



1 There are no extra-bulbar salivary glands in Nautilus, but intra-bulbar glands in relation with Owen's 

 faucial follicles have been described by Griffin (Zool. Bull. 1897, Vol. i. p. 149, fig. 4). Compare also 

 Joubin, L., " Recherches sur la morphologie comparee des glandes salivaires. Glandes salivaires des Cephalo- 

 podes." Arch. Zool. Exper. (2) Tome v. Suppl. 1887, Me'm. in. 



2 There are simple valves (noted by Owen) at the bases of the branchio-cardiac trunks and a semilunar 

 valve at the root of the truncus arteriosus. 



102—2 



Fig. 8. View of proximal branches of the systemic 

 aorta, from above. 



1. Truncus arteriosus (leaving the pericardium). 

 Main hepatic artery. 

 Gastric artery. 

 Right hepatic artery. 

 Left hepatic artery. 

 Posterior proventricular artery. 

 Right posterior columellar artery. 

 Left posterior columellar artery. 

 Right pallio-nuchal artery. 

 Left pallio-nuchal artery. 



2. 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 

 10. 



