ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 761 
capsule. This column passes from above downwards and outwards, and for a few 
sections divides the auditory chamber into a larger ventro-internal cavity, open widely 
_ by the auditory foramen, and a smaller closed dorso-external cavity. As, of course, the 
connection is only a rod, the division of the auditory chamber into two, seen in a few 
sections, is apparent but not real. This column has been overlooked by all writers on 
the myxinoid skeleton except Parker, who figured it in his sections but failed to under- 
stand its real nature. Rerzivus (op. cit.) also found it, and states that it corresponds in 
direction to a continuation of the bridge of soft cartilage described below as connect- 
ing the auditory capsule with the hyoid arch. This is quite true, but whether the fact 
has any significance cannot be determined by adult anatomy. It must, however, be 
emphasised that the two structures represent two different kinds of cartilage. The 
dorso-external wall of the auditory capsule behind fuses by means of a very short but 
wide bridge of soft cartilage (forming the posterior boundary of the second fenestra) 
with the dorsal extremity of the hyoid arch. Where this fusion occurs the entire 
thickness of the capsule consists of soft cartilage. There is, in fact, here a ragged oasis 
or plug of soft cartilage in the wall of the capsule. In front, the dorso-external surface 
of the capsule forms the dorsal boundary of the second fenestra of the skull (f-”).* The 
anterior margin of the capsule fuses with the posterior extremity of the trabecula. 
‘ Trabecula” (figs. 1 and 2, tr.).—The trabecular bar fuses behind with the auditory 
capsule, as just described. It then passes almost straight forwards as a stout rod of 
_ hard cartilage, its lateral border behind being fused by a very short but wide bridge 
of soft cartilage with the dorsal border of the superior process of the pterygo-quadrate. 
At this region the trabecula itself is invaded by numerous nests of soft cartilage. The 
above bridge forms the ventro-anterior boundary of the second fenestra of the skull, 
and the posterior boundary of the first (f."). In front, the outer edge of the trabecula 
forms the entire dorsal or internal boundary of the first fenestra. At its anterior extremity 
the trabecula becomes gradually converted into soft cartilage, PaRKER’s figures of the 
distribution of the hard and soft cartilage at this region being inaccurate according to 
my dissections and sections. From its inner border in front the trabecula despatches 
downwards and forwards a rod of soft cartilage (the sustentaculum of NrEuMaYER), which 
fuses with the central expanded portion of the hypophysial plate. This cannot be fully 
shown in such a view as illustrated in fig. 2, owing to the perspective. The trabecula 
finally bends outwards to fuse with the posterior extremity of the palatine bar, which 
here consists entirely of soft cartilage also. 
An interesting observation recorded by ALuis is that in a “12 mm.” ¢ Bdellostoma 
the “pharyngeal basket is nowhere connected with the trabecula,” the bridges of soft 
cartilage described above being absent. From the fact that these bridges are of soft 
cartilage (PARKER, however, figures the anterior one as hard cartilage in Bdellostoma), 
ALLIs concludes that they must represent later additions. On the other hand, the fact 
* All the fenestrz are closed by fibrous membranes or tissue. 
+ This measurement is obviously erroneous. 
