ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 677 



there were only a few nests of hard cartilage here and there, and hence the whole of 

 it is coloured blue in figs. 1 and 2. 



With regard to the basal plate, reference must first be made to Schaffer's 

 description and figure's (28), published almost simultaneously with my own. His 

 results are practically identical with mine, the only differences being such as may 

 easily be explained by individual variation. Thus, for example, he does not describe 

 the median zone of soft cartilage in the middle segment extending from one end of it 

 to the other, although I have found it do so both in dissections and serial sections. 

 He says, in fact : " Die Knorpel der zweiten Reihe [middle segment] bilden ebenfalls 

 ein einheitliches Stiick, welches allerdings in der Medianlinie eine weichknorpelige 

 Naht besitzt, welche jedoch den rostralen Band des hinteren Mittelstiickes nicht 

 erreicht" (p. 242). Schaffer states that the pseudo -cartilage "rails" (7, pp. 772-3) 

 may be regarded as independent skeletal pieces, since they are enclosed in a fibrous 

 membrane : " So bildet es an der dorsalen, konkaven Flache des rinnenformigen 

 ' Zungenbeins ' dort, wo es bereits hartknorpelig geworden ist, zwei dlinne, 

 leistenformige Aufsatze, welche von der Masse des Zungenbeinkiels entspringend, 

 zunachst iiber den freien, dorsalen Randern desselben verlaufen, dann in die Rinne des 

 hartknorpeligen Zungenbeins hineinriicken und hier parallel gegen den rostralen Rand 

 nach vorn ziehen, um sich dort miteinander und mit dem kissenartigen Uberzug zu 

 vereinigen. Sie dienen zur Vertiefung der Rinne, in welcher, wie in einer Schlittenbahn, 

 die Sehne des Retractor linguae [and also the dental apparatus] gleitet" (pp. 249-250). 



The relative proportions of the three segments of the basal plate (b.p. x , b.p. 2 t 

 b.p. s ) do not appear to vary very much. Thus, to take three cases at random, 

 omitting the anterior pad of pseudo-cartilage, and regarding the whole plate as a unit 

 of measurement, we get the following results from Schaffer's figures (A), from the 

 figure in my first part (B), and from my large series of sections (C). The three 

 segments of the basal plate are taken from before backwards. A, "19, '21, '6 ; B, "18 1, 

 '166, '652 ; C, '194. '184, '621. It is thus seen that the anterior segment is the most 

 constant. 



The posterior segment of the basal plate (b. p. 3 ), differing so markedly from the 

 others, has attracted much attention. Ayers and Jackson (2, p. 205) state that " it is 

 quite evident that the third segment is not a true cartilage, but is formed by a 

 chondroidal modification of the tendon of the 'constrictor' muscle [copulo-copularis]." 

 Again (3, p. 10) : " Of these, the posterior is composed, not of true cartilage, but of a 

 chrondroidal tissue, and is certainly not to be considered as homologous with any part 

 of the visceral arches. It is merely a condensation of the tendinous tissue in the 

 median ventral raphe of the constrictor musculi mandibuli." Schaffer (26) regards the 

 posterior segment as a true sesamoid formation in the tendon of the retractor linguae 

 (longitudinalis linguae). I presume Schaffer means the copulo-copularis, since it is 

 obviously impossible that the retractor muscle can have anything to do with the basal 

 plate ; but he repeats the statement in a later paper (27). Assuming, as appears to me 



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