110 EDWARD PHELPS ALLIS, JR. 



and the ligamentum hyoideo-mandibulare externum of Goodey's 

 ('10) descriptions of this fish, this ligament of Chlamydoselachus 

 apparently being the homologue of the ligamentum mandibulo- 

 hyoideum of my descriptions of Amia (Allis, '97). Antero-ventral 

 to this ligament the artery sends a commissural branch outward 

 around the ventral edge of the mandibula and then through the 

 lateral edge of the musculus intermandibularis, where it falls into 

 the afferent mandibular artery just above described. Postero- 

 dorsal to the ligament a branch (a, fig. 2) is sent dorso-anteriorly 

 across the internal surface of the mandibula toward the angle 

 of the gape of the mouth, where it separates into two portions; 

 a small ventral one which runs forward along the dorsal edge 

 of the internal surface of the lower jaw and a much larger dorsal 

 one which runs forward along the ventral edge of the internal 

 surface of the upper jaw. This latter branch, on both sides of 

 the head of this specimen, passes immediately anterior to a rel- 

 atively deep tubular pocket, or recess, of the lining membrane 

 of the mouth cavity which, beginning slightly posterior to the 

 angle of the gape, extends dorso-posteriorly toward the quad- 

 rato-mandibular articulation. This pocket lies along the exter- 

 nal surface of the hind end of the palatoquadrate, between that 

 cartilage and those fibers of the musculus adductor mandibulae 

 that pass uninteruptedly from the upper to the lower jaw. 

 Posteriorly it ends blindly, its blind end being attached to liga- 

 mentous tissues which, continuing on in the line prolonged of the 

 pocket, are attached to the hind (distal) end of the palatoquad- 

 rate. The pocket thus lies morphologically anterior to the 

 palatoquadrate, in the relation to that cartilage that a persisting 

 remnant either of the mandibular cleft or of a premandibular 

 cleft would have, and its position, posterior to the musculus 

 adductor mandibulae, is not unfavorable to its being a remnant 

 of either of those clefts, for the adductor muscle, if it be derived 

 from the superficial constrictor of the mandibular arch, could 

 readily, when it slipped from the external (actually posterior) 

 edge of the arch on to its anterior (actually lateral) surface, 

 have acquired a position superficial, and hence morphologically 



