ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 06 
owing to a covering fold of mucous membrane, and this explains some of the so-called 
variations in the number of teeth referred to by systematists. As pointed out by AYERs 
and JACKSON, it is quite a simple matter to obtain excellent microtome sections of the 
teeth, provided they are embedded in celloidin. And even with paraffin embedding I 
have serial sectioned three heads of moderately sized Hags (about 25 cm.) without in 
any way damaging the teeth or losing a section. 
J. MULEr’s description of the dental skeleton of Bdellostoma calls for no comment, 
except that he does not figure or mention the small perforation transmitting the 
dental nerve, but refers to it in his later work on the nerves. It is not described by 
Ayers and Jackson or by Parker in bdellostoma, although the latter author figures it 
in Myxine. Parker also describes and figures in Myaine a long median rod of soft 
cartilage projecting backwards from the posterior arch, but not found in Bdellostoma, and 
in the latter type he describes the anterior arch as formed largely of hard cartilage. 
Neumayer figures and describes the two arches in Myxine as unfused and only joined 
up by connective tissue. The slender cartilaginous connections of the adult may well 
be secondary. 
J. SKELETON OF THE VELUM OR PHARYNGEAL VALVE. 
(Fig. 16. Also figs. 2 and 1.) 
The skeleton of the velum, of which J. MULLER says nothing similar is known in the 
animal kingdom, commences, as the external lateral velar bar (e. 1. b.), by a club-shaped 
ventrally scooped out head (fig. 16) of hard cartilage at the posterior end of the third 
fenestra of the skull. This is connected near its extremity by a short bridge of soft 
cartilage (e. /. b.’) arising from the inner or ventral edge of the bar, which fuses near the 
ventral border of the fenestra with the junction of the inferior process of the pterygo- 
quadrate with the hyoid arch. This bridge is not present in Bdellostoma, according 
to Ayers and Jackson, but the head of the external bar is connected by ligament only 
with the pharyngeal wall. J. Mi.uer’s description of Sdellostoma more nearly 
approaches the Myxine condition, there being precisely the same connection, but 
formed, however, partly by a cartilaginous articular tubercle and partly by ligament. In 
Myzxine, Parker says that the bar is ‘‘ joined to the general thickness of cartilage in the 
hind part of the oval fenestra,” but does not state the nature of the junction ; whilst in 
dellostoma he says that it is “confluent with the hyomandibular.” His figures give 
no assistance on this point. 
At first the external bar lies above and external to the pharynx and anterior to the 
base of the velum, but it soon assumes a position internal to an anteriorly directed 
blind diverticulum of the gut which surrounds it on all sides except internally. This 
diverticulum then fuses below the bar with the naso-palatine duct or hypophysial 
canal, and above the bar it approximates very closely to the same canal but does not 
fuse with it. Asa result the bar is surrounded on all sides, except for a very narrow 
