726 MR FRANK J. COLE 



with the first branchial arch ; (c) the greater part of the fibres, however, are inserted 

 into the dorso-lateral free border of the U-shaped posterior segment of the basal plate 

 from its commencement to the beginning of the taper, i.e. to the commencement of 

 the copulo-copularis. The whole insertion extended over 8 mm. 



In the sections the insertion of the first division of the constrictor pharyngis was 

 as follows : — the anterior fibres were wedged into the angle formed by the fusion of 

 the first and second branchial arches ventrally, but the insertion was clearly more into 

 the first than into the second branchial arch. The insertion then leaves both arches 

 and passes on to the dorso-external surface of the posterior segment of the basal plate 

 immediately below the second branchial arch. As, however, the latter rises, the muscle 

 follows it until it reaches its characteristic insertion into the summit of the posterior 

 segment immediately above and internal to the insertion of the copulo-quadratus 

 superficialis. 



Second Division (c.p".).- — This may be distinguished from the first division by its 

 different insertion. In the sections, however, the separation of these two divisions 

 was not so obvious, but I was able to establish it, especially as the fibres of the first 

 division appeared to be larger than those of the second. The second division is not 

 so compact as the first, and consists of a number of discrete fasciculi, which, however, 

 continue the same origin backwards, i.e. from the superficial internal fascia of the 

 parietalis, not far from the middle line. The origin, in the specimen above, extended 

 over 16 mm. The fibres, slightly converging, pass sharply forwards and somewhat 

 downwards and outwards, to be inserted into the external fascia of the dorso-lateral 

 region of the copulo-copularis from its pointed extremity backwards. The insertion 

 extended over 15 mm. 



Third Division (e.p'".). — This is not present in Bdellostoma, unless, as seems certain, 

 J. Muller's first loop of the constrictor of the gills partly or entirely represents it. 

 The third division is not so sharply defined as the other two, and the distinction may 

 be difficult to draw in occasional specimens. It is, however, more compact than the 

 second division, and has often a different origin behind and a slightly different insertion. 

 In the sections, I was not able to distinguish between the second and third divisions, 

 as there was no difference either in the origin or in the insertion. In the specimen 

 shown in fig. 3 (but which, however, seems to be exceptional), about the first half of 

 its fibres continued the previous origin backwards from the superficial internal fascia 

 of the parietalis, as in the first and second divisions. The posterior half, however, 

 arose from the ventral surface of a ligamentous sheet despatched forwards from the 

 constrictor of the gills to the dorsal superficial internal fascia (cp. fig. 3). The whole 

 origin extended over 11 mm. Hence, whilst the anterior fibres of this division 

 pursued a course similar to that of the second division, the posterior fibres passed at 

 first forwards over the afferent duct of the first gill pouch, and internal and dorsal to 

 the pouch itself, and then downwards and outwards to reach their insertion. All were 

 inserted into the external fascia of the copulo-copularis of the dorsal region, near the 



