— 
648 ALLIS. [Vou. XII. 
the first and second arches in Esox, and is considered by Vet- 
ter as part of the obliquus of the second arch. 
The hypobranchials of the third and fourth arches are much 
flatter than those of the first and second. Their lower ends are 
bent backward and upward slightly, but there is no twist or 
lateral compression to the bone, and at the bend or angle on 
the front edge of each there is a small process directed down- 
ward and forward, approximately in the line of the anterior 
edge of the piece, to form a second articulation or connection 
with the basibranchial. Both distal ends of the element are 
capped with cartilage, as is also the proximal end, the proximal 
cap of the fourth hypobranchial and that on the larger of its 
distal ends being often continuous along the hind edge of the 
element, the bony portion of the element having in such cases 
a semicircular form, the arc of the circle directed backward. 
The two hypobranchials are appreciably grooved, on their ven- 
tral surfaces, only at their outer ends and mainly in the cartilagi- 
nous cap of the piece. The lower end of the groove lies or 
opens between the two articular ends of the element. At the 
base of the anterior articular end of each element, on its ante- 
rior edge, there is a slight process for the attachment of the 
interarcual ligament, and there is a similar process, or more 
properly eminence, on the posterior edge of the third hypobran- 
chial, where the proximal cartilaginous cap joins the bony part 
of the element, and on the fourth hypobranchial in the proximal 
cartilaginous cap itself, the process on this last piece being 
sometimes so pronounced that it forms an angular projection 
overlapping ventrally the end of the fifth ceratobranchial. 
Similar processes are indicated in the proximal cartilaginous 
caps of the third and second hypobranchials. The bony portion 
of the fourth hypobranchial is formed concentrically around the 
point of attachment of the interarcual ligament between that 
arch and the third arch, and in the bone of the third hypo- 
branchial is also indicated a similar concentrical arrangement 
around the point of attachment of the ligament between that 
arch and the second. The ligament between the fourth and 
fifth arches is inserted along the entire anterior edge of the 
distal cartilaginous cap of the fifth ceratobranchial, and extends 
