422 HARRIS HAWTHORNE WILDER ON 
culare,” thus producing a confusion of terms. The spleniale is a thin scale of oval shape, 
presenting a slightly concave inner, and a slightly convex outer surface. Along the side 
of the former is attached a row of teeth, and the outer surface shows a longitudinal divi- 
sion into an area covered by the den- 
tale and a free area, which contributes 
a little to the formation of the outer 
surface of the mandible. 
The oval shape and lack of detail 
INNER ASPECT 
‘ Outer ASPECT 
Fig. 21. Two views of right spleniale. X 8. Contact sur- oipthis hove render is oe 
faces with other bones are designated by an x. P. ant., processus ficult, but its outer and inner surfaces 
anterior. are very evident, and in most cases 
the anterior end is prolonged into a 
point, while the posterior end is rounded. In its natural position it rests by its lower mar- 
gin upon the upper edge of the angulare just anterior to the coronoid process, and the 
ventral half of its outer surface is closely applied to the dentale. 
The hyobranchial apparatus. — This consists of a series of sixteen pieces, all but 
one being entirely cartilaginous, and representing four of the original visceral arches. 
Their arrangement is so easily seen from plate 65, figure 12, that a verbal description of 
the parts would seem almost superfluous. The system is seen to contain two median 
pieces, universally designated as the first and second basibranchials, and referred to the 
first and second branchial arches respectively, of which they form the middle pieces or 
copulae. Of these, the second is ossified in the adult and its free posterior end usually 
terminates in a rounded extremity, although an occasional individual shows a division at 
the end into a two or three forked form, such as occurs normally in Siren. The hyoid 
arch, which is attached to the anterior end of the first basibranchial, consists of two pieces, 
an inner hypohyal and an outer ceratohyal. The first branchial arch is the best devel- 
oped of all the branchial arches, consisting of two nearly equal pieces, cerato- and 
epi-branchiale 1, the first of which is directly connected with both the first and second 
basibranchial and with its opposite. The second branchial arch consists of a smaller 
epibranchial, and a rudimentary ceratobranchial, reduced to a nodule of cartilage lying 
upon the inner side of the distal end of the first ceratobranchial. An epibranchial smaller 
than the previous one is the only remnant of the third branchial arch. 
In life the distal ends of the three epibranchials support the external integumental 
branchiae and furnish attachment for some of their muscles, a circumstance which has 
often misled investigators as to the true homology of these purely integumental organs, 
since the location suggests a definite phylogenetic relation to the internal gill system. 
In the intervals between these epibranchials there occur, even in the adult Necturus, two 
