778 MR FRANK J. COLE 
breach, by a double mucous enclosure. At about section 700 in the chart (fig. 16) 
the hard cartilage becomes gradually replaced by soft cartilage, of which the whole 
of the remainder of the velar skeleton is formed. Subsequently the fused diverticulum 
and hypophysial canal join up with the wall of the pharynx in such a way that 
the ventral wall of the canal portion and the inner wall of the diverticular portion 
first fuse with the dorso-lateral wall of the pharynx, and then the product of this 
fusion disappears. In this way the connection between the cavities of the three 
structures is established. It follows, therefore, that the velum is a double structure, 
each half supported by the external lateral velar bar and each formed as an evagination 
of the dorso-lateral wall of the pharynx. These two halves are connected by a dorsal 
median double partition, called by J. MULLER the “ suspensory ligament” of the velum ; 
and a transverse section of this region would suggest (of course, wrongly) that the 
velum had been formed by a median dorsal invagination of the roof of the pharynx, 
and that this invagination had then sent out on each side into the cavity of the pharynx 
a lateral extension. 
The external bar now gives off the internal lateral velar bar (7. 1. b.), which courses 
laterally in the velum internal and ventral to the external bar. Parker figures and 
describes the internal bar as independent of the external in Myaxvine ; and although this 
condition is sometimes suggested, as on the right side of fig. 2, I have always found 
it fused with the external bar, and as such Parker figures and describes it in Bdellostoma. 
The two internal bars subsequently become connected by a transverse bridge, the 
anterior transverse velar bar (a. t. v. b.), which traverses the now enlarged isthmus 
connecting the lateral wings of the velum. From this transverse bar three processes 
arise, as follows: (1) a pair of narrow rods which pass forwards and gradually ascend 
dorsally im the median partition until they reach the roof of the pharynx, where they 
form a portion of the swprapharyngeal skeleton (sp. sk.’, fig. 16) suspending the velum 
from the dorsal pharyngeal wall. Here each rod gives off externally a long blind 
process, which passes outwards and backwards over the roof of the pharynx, the main 
stem being then continued almost straight forwards, but slightly outwards, below the 
notochord and over the pharynx; (2) a narrow rod which arises from the dorso- 
posterior surface of the bridge, and passes forwards and upwards in the median 
partition until it reaches the roof of the pharynx, where it constitutes the remainder 
of the suprapharyngeal skeleton (sp. sk.”). It at once bends sharply backwards on 
itself, and extends posteriorly as a wide plate in the middle line under the chorda 
and over the pharynx. Behind the suprapharyngeal skeleton the position of the 
longitudinal bars is reversed, the external bar having now crossed over above the 
internal so as to occupy the more median position. In Bdellostoma, according to the 
figures of J. MUnier, Parker, and AvERS and Jackson, there is no such crossing; but 
I suspect the drawings of these authors must be diagrammatic in this respect, or the 
velum must be widely different in Bdellostoma. The two internal bars are finally 
connected up a second time by the posterior transverse velar bar (p. t. v. b.), which 
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