ON THE GENERAL MORPHOLOGY OF THE MYXINOLD FISHES. 723 



inserted into the scooped-out hollow on the ventral surface of the head, and also into 

 the margins of the external lateral velar bar. 



Like the velo-quadratus, the velo-spinalis is a small-fibred muscle. It has a long 

 extended origin from the ventro-lateral surface of the skeletogenous layer of the 

 notochord, commencing just behind the posterior extremity of the parachordal carti- 

 lages, and internal to the anterior portion of the origin of the first division of the 

 constrictor pharyngis. In the sections the postero-ventral border of the origin was 

 connected by a fibrous cord with the dorso-external margin of the anterior extremity 

 of the anterior connecting process of the suprapharyngeal skeleton (cp. Part I., fig. 16, 

 sp. sk'., about section 780). J. Muller, in the description of his plates (p. 317), also 

 mentions this connection, and in fact there describes the muscle as passing only 

 between the two portions of the velar skeleton, and not as arising from the chorda. 

 This, however, is figured and also described in the text. P. Furbringer describes the 

 chordal end of the muscle as its insertion ; but as this end is obviously the fixed point, 

 this is not permissible. 



From its origin the velo-spinalis, with fibres converging, passes at first downwards, 

 and then bends sharply so as to course forwards, outwards, and downwards in a gentle 

 curve as a small compact cylindrical muscle, lying internal to the cranio-hyoideus, and 

 separated from the velo-quadratus by the pharyngeal diverticulum described on p. 777 

 of my first Part. The insertion, however, is effected immediately anterior to this 

 diverticulum, and there the two muscles meet and are closely associated. After a 

 course of 5 mm. in a 35 cm. Hag, the velo-spinalis was inserted into the dorso-external 

 surface of the head of the external lateral velar bar where this appears in the third 

 fenestra of the skull, and seems at first sight to represent the posterior continuation of 

 the external fibres of the middle division of the velo-quadratus. In the sections it was 

 inserted mainly into the dorso-external margin of the bar, but as it approached the 

 extremity of the head it extended somewhat on to its external surface. Hence the 

 velo-spinalis appears in the third fenestra of the skull immediately behind the middle 

 division of the velo-quadratus. This portion, however, has been cleared away in 

 figs. 3 and 11. 



According to P. Furbringer, the velo-spinalis displays the velum laterally by 

 drawing the head of the external lateral velar bar inwards, and in that way inducing a 

 general outward rotation of the bar (but cp. the function of the velo-quadratus). 



27. M. cranio-hyoideus. (Figs. 3, 11, c.h.) 

 J. Muller, Erster Constrictor des Schhmdes (pp. 260, 324). 



P. Furbringer, on the score of innervation, objects to J. Muller regarding this 

 muscle as a division of the extensive constrictor pharyngis. There would, however, be 

 a very strong resemblance between these two muscles if it were not for the fact that 



TRANS. ROY. SOC. EDIN., VOL. XLV. PART III. (NO. 26). 103 



