In the bony ganoids, as s tated above, th e process is n o t found as a p a rt of th e quadrate. I t
is, however, elsewhere represented in both Amia and Lepidosteus. In Amia, it has fused with th e
symplectic and forms an irregular articular head of th a t bone (Allis, 97 a, pi. 20, Fig. 4); while in
Lepidosteus it is th e preoperculum of Parker’s (’82 b) descriptions, and the interoperculum of Collinge’s
(’93) descriptions. In Amia th e relations are all too evident to leave any doubt as to this homology;
and comparison of Lepidosteus with Amia leaves no doubt as to this la tte r fish. The bone, in Lepidosteus,
is n o t properly shown by either Parker or Collinge; the important features omitted being
th a t the bone has an articular head smaller b u t similar to th a t in Amia, and th a t this head articulates
with a facet oh th e posterior surface of a ventrally projecting portion of th e articular head of the
quadrate. The disappearance of a relatively small intervening wall of quadrate bone, or a slight
shifting of th e parts together with a concomitant fusion of the bone with th e adjoining symplectic,
would produce the conditions found in Amia; while a fusion of th e bone with th e quadrate, instead
of with the symplectic would produce the usual teleostean quadrate. A further fusion of th e symplectic
with the quadrate would apparently produce th e conditions found in th e Siluridae and those
others of th e Physostomi in which th e process of th e quadrate seems absent; th u s leaving only th e
Lophobranchii as apparent exceptions to the general rule. The bone would seem to be, judging from
the conditions found in Lepidosteus, a bránchiostegal ray related either to th e quadrate or to the
mandible.
In Polypterus this process of the quadrate is neither shown ñor described, So far as I can
determine, and in this fish there is also, according to Traquair (’70)¡, no symplectic.
I t m ay here be s tated th a t Gymnarchus, in th e fusion of th e symplectic, th e posterior process
of th e quadrate and th e body of th e la tte r bone into a single piece, and in th e intimate and rigid
nature of th e attachment of the entire suspensorial apparatus to th e cranium, approaches th e
amphibian condition, as it does also, as I (’04) have lately shown, in the possession of an auditory
apparatus resembling th e amphibian ear.
M E T A P T E R Y G O I D .
The metapterygoid consists of a thick quadrant-shaped endosteal portion, and three th in
b u t extensive flanges th a t appear to be of purely membrane origin. The curved ventral edge of the
quadrant-shaped portion is directed ventro-anteriorly and is everywhere bounded by cartilage, a
narrow band of which separates it from th e dorsal edge of th e quadrate* The angle of the quadrant
is directed dorsally, and this angle is apparently th e centre of ossification for the endosteal body
of th e bone and also for the apparently membrane flanges. From this angle a slender process arises,
and projects dorso-anteriorly in th e line prolonged of th e hind edge of the body of the bone. This
process is more th an one half as long as th e h ind edge of the bone, and has the same general appearance
and color as th e body of th e bone. I t m ay, therefore, also be of endosteal and n o t of membrane origin.
One of the three membrane flanges is a th in web of bone th a t fills th e angle between th e anterior
edge of this slender process and th e dorso-anterior edge of the body of th e bone. The other two
flanges arise from th e full length of th e hind edge of the bone, th a t hind edge including the slender
process as well as th e body of th e bone. The two flanges project dorso-posteriorly, and, spreading
somewhat, enclose between them a Y-shaped space* This space lodges and gives insertion to a
deeper portion of th e levator arcus palatini, the superficial portion of th a t muscle lying external
to the external flange. The V-shaped space also lodges th a t terminal portion of the external carotid
th a t runs downward and backward to fall into the arteria hyoidea, as already described. The hind
edge of the external one of these two flanges abuts against, and is firmly bound to, the anterior edge
of the ventral half of th e shank of th e hyomandibular, the dorsal portion of the corresponding edge
of the ‘internal flange being similarly connected with, b u t not abutting against, the anterior edge of
th a t th in portion of the hyomandibular, apparently of membrane origin, th a t lies between the anterior
articular process and th e shank of the bone. The external flange is quite undoubtedly an
ossification of th e metapterygoid membrane of Arnia, the thickened, process-like portion of the
flange being the homologue of the metapterygoid process of th a t fish (Allis, ’97, p. 557).
Across the anterior one third to two-thirds of the internal surface of the body of the
metapterygoid, at about the middle of its length, the entopterygoid extends, that bone lying at
an angle to the metapterygoid. The V-shaped space between the two bones is filled by, and gives
insertion to, a portion of the adductor arcus palatini.
E C T O P T E R Y G O I D .
The ectopterygoid is a slender bone, with two sharply pointed limbs lying a t an obtuse angle
to each other. From the angle between the two limbs a th in and irregular process projects dorso-
posteriorly, lying against, th e internal surface of th e palato-quadrate cartilage, and, beyond th a t
cartilage, against th e internal surface of the metapterygoid. The ventro-posterior limb of the bone
is the shorter of th e two, is bevelled and fits against the internal surface of the anterior edge of the
quadrate. The dorso-anterior limb fits upon the dorsal edge of th e posterior portion of the ventral,
ectosteal flange of the palatine, and although b u t a thin and slender bone is grooved its full length,
on its dorsal surface. This little groove lodges the ventral edge of a slender and rod-like portion of
the palato-quadrate cartilage, which connects th e cartilages of th e palatine and quadrate regions,
and, mesial to th a t rod of cartilage, lodges the ventro-lateral edge of the anterior portion of the
entopterygoid.
E N T O P T E R Y G O I D .
The entopterygoid is a V-shaped bone, one limb of the V being small and the other large,
the point of the V directed ventro-laterally. The small lateral limb lies against the internal surface
of the anterior portion of the metapterygoid, and against th e same surface of the adjoining portion
of th e palato-quadrate cartilage. The larger mesial limb is a thin smooth and delicate, b u t relatively
darge plate of bone, the ventral edge of th e anterior portion of which lies in the groove on the dorsal
surface of the dorso-anterior limb of the ectopterygoid, and there rests against the inner surface
of th e palatine bone and the same surface of the rod-like remnant of th e palato-quadrate cartilage.
Posterior to the la tte r cartilage, the ventral edge of this plate rests against, and is bound by tissue
to, the internal surface of the metapterygoid. This mesial limb of the entopterygoid is closely applied
to the ventral surface of th e anterior portion of the adductor arcus palatini muscle, and its dorso-
mesial edge is connected, by th e lining membrane of the mouth cavity, with the ventral surface of
th e parasphenoid.
The adductor arcus palatini has, as already stated, a long surface of origin, this surface beginning
on the lateral surface of the ascending process of the parasphenoid and on adjacent portions
of the prootic and from there extending forward along the lateral surface of the body of the parasphenoid
as far as the antorbital cartilage. From this long surface of origin the broad muscle runs
Zoologies. Heft 57. g