3IO CHORD ATA. 



which is the mouthy surrounded by four pairs of small Inicial 

 cirri. Above the mouth is a small median aperture usually 

 termed the nasal opening. It leads into a tube, the 

 pituitary sac, which also has an internal opening into the" 

 pharynx. 



The single olfactory sac opens into the pituitary sac near 



its external aperture. The mouth is situated at the base of 



a suctorial buccal funnel, on the dorsal wall of 



imen y. ^,]^-^j^ -g ^ large median horny tooth. Other 



horny teeth are attached to a large tongue which is moved 



by enormous muscles. 



Myxine is an active carnivorous animal and often devours 

 fish caught on the lines. It is indeed frequently so caught 

 itself. The edges of the buccal funnel are said to form a 

 sucker, and the movements of the tongue serve to rasp the 

 flesh of its victim. 1 he mouth passes into a pharynx 

 continued backwards into a oesophagus. The pharynx 

 has six pairs of lateral openings which pass outw^ards 

 into large branchial sacs (or gill-pouches) containing the 

 gills. From each of these a canal leads back- 

 wards. Those of each side unite to open by a 

 single branchial aperture situated ventro-laterally. Behind 

 the last branchial sac the oesophagus has a duct on the left 

 side (the oesophageo-cutaneous duct) leading directly to the left 

 branchial aperture. When the mouth is being employed 

 the respiratory current passes through the pituitary sac to 

 the gills. The oesophagus expands into an intestine \^ hich 

 receives a bile-duct from a simple bilobed liver. There is a 

 small gall-bladder. The intestine terminates ventrally in an 

 anus. 



The notochord consists of a skeletal chordoid rod running 

 from below the mid-brain to the tip of the tail. It is sur- 

 rounded by a thick sheath. A membranous 

 sheath also surrounds the nerve-cord. There 

 is no trace of a vertebral column. Cartilage is found in 

 rings supporting the '* nasal passage," and the buccal cirri 

 are supported by cartilages. Under the brain there lies a 

 ventral cartilaginous portion of a cranium, completed dor- 

 sally by membrane. A trace of visceral arches may be 

 represented by a subocular bar and other cartilaginous 

 structures connected with it, united wdth the cranium. 



