ON THE GENERAL MORPHOLOGY OF THE MYXINOID FISHES. 725 



cranial framework or with the basal plate. Its vestigial condition on one side described 

 above supports this view. 



28. M. constrictor pharyngis. (Figs. 2, 3, 11, c.p'., c.p"., c.p'".) 



J. Muller, Constrictor des Schlundes [second and third portions] (p. 260). Ziveiter Con- 

 strictor des Schlundes. Dritter Constrictor des Schlundes (p. 324). Constrictor 

 pharyngis (p. 276). 



Alms, Constrictor oesophagei (p. 334). 



A very long powerful muscle, which, perhaps arbitrarily, may be divided into three 

 sections which I have found to be separated by small breaks, as shown in fig. 3. The 

 second and third divisions, however, may not be sharply differentiated. 



First Division (c.p 1 .). — A few of the most anterior fibres may arise from the 

 posterior extremity of the auditory capsule. In the sections none of the fibres arose 

 from the capsule, but the origin commenced on the tough vascular fascia covering the 

 post-auditory parachordals laterally. From here the origin extends downwards, back- 

 wards, and slightly outwards, first passing obliquely across, and at the same time 

 arising from, the dorso-lateral surface of the notochord, until it arrives at the lateral 

 surface of the chorda, and in a 34|- cm. Hag, 2 mm. from the exposed ventral margin 

 of the latter. It thus reaches the place where in transverse section the inner free 

 surface of the parietalis meets the chorda. In front, this is about half way down the 

 latter, but behind, the parietalis more and more involves the chorda, although it never 

 completely encloses it ventrally, even in the tail. 



The origin now passes straight backwards parallel to the chorda, and arising from 

 the superficial internal fascia of the parietalis — at first in the angle formed by this 

 muscle with the chorda, but behind moving out laterally away from the latter. In the 

 above Hag the origin extended over an area of 22 mm. From the origin the fibres 

 strongly converge, most of them passing forwards and downwards in a curve round 

 the lateral wall of the gut. The anterior fibres describe a graceful curve, with the 

 concavity looking forwards, and the muscle covers the pharyngeal basket externally 

 from the first branchial arch backwards, except for the most ventral third of this arch. 

 The general appearance of this part of the muscle closely resembles an open fan. The 

 insertion (hidden by the copulo-quadratus superficialis) is as follows : — (a) the fibres form- 

 ing the most anterior sixth are inserted into the posterior surface of the most ventral 3 

 mm. of the first branchial arch, i.e. where it fuses with the middle segment of the basal 

 plate. Cp. the connection of the cranio-hyoideus, the hyo-copulo-palatinus, and the 

 hyo-copulo-glossus with this portion of the first branchial arch ; (6) a few fibres are 

 inserted into the dorso-external surface of the root of the lower division of the second 

 branchial arch (when present, as I now believe it generally is *) just where it fuses 



* Cp. Part I. p. 763. Since my first Part was published I have dissected a Myxine in which the lower division 

 of the second branchial arch fused with the upper exactly as shown for Bdellostoma by Ayers and Jackson in their 

 fig. 6. On pp. 763-4 of my first Part I state that this fusion has never been seen in Myxine. It is, hence, interesting 

 to record it now. 



