In larvae 55 and 80 mm in length, I find, occupying th e place of th e alisphenoid bone of
Parker’s descriptions, a V -shaped process of th e parasphenoid which embraces the mesial edge of an
anterior plate-like process of the prootic cartilage. This process of the prootic cartilage occupies th e
place of, and certainly is th e basipterygoid process of Parker’s descriptions, b u t it has a short free
mesial edge not shown by Parker. The anterior edge of the V-shaped process of th e parasphenoid
is closed b y a rounded union of the plates th a t form its two limbs, and th e limbs are here both
short, extending laterally only about one th ird th e width of th e cartilage. This rounded anterior
edge of th e process, and the corresponding edge of th e cartilage b eyond it, together, give articulation
to th e metapterygoid. The point of the V of th e V-shaped process is directed mesially toward the
lateral edge of th e parasphenoid, b u t it does not, in its anterior portion, quite reach th a t edge.
Posteriorly i t meets and fuses with the edge of the parasphenoid, th u s becoming a p a rt of th e
ascending process of th a t bone. The dorsal (internal) limb of th e V there vanishes, while th e
ventral (external) limb becomes prolonged into th a t ta ll plate of th e ascending process of th e
parasphenoid th a t lies against the external surface of the prootic cartilage. In 19 mm and 25 mm
specimens, which I have also examined, the internal limb of th e V-shaped process has hot yet
developed, the external limb alone being found. The V-shaped process of older specimens is
thus, in these young larvae, simply a plate-like p a rt of the ascending process of the parasphenoid
which, projecting forward, forms th e lateral boundary of a narrow space, or notch, between itself
and th e lateral edge of th e body of th e parasphenoid. Through this notch th e efferent pseudobranch-
ial a rte ry runs upward, and then turns mesially between th e body of the parasphenoid and the
overlying cartilaginous basis cranii, to join and completely fuse with th e internal carotid. Im mediately
posterior to the notch, th e ventro-mesial edge of th e base of th e basipterygoid process
of th e prootic cartilage fuses with th e ventral surface of th e lateral edge of a short band-like portion
of th e cartilage of th e region, this la tte r cartilage bounding th e space in which th e hypophysis lies.
Posteriorly this band is continuous with th e parachordal cartilage, while anteriorly th e lateral end
of its nearly straight anterior edge is continuous with th e thickened ventral edge of th e cartilage
of th e alisphenoid region; th a t thickened edge of th e alisphenoid cartilage being continuous, an te riorly,
with th e hind end of a median portion of th e trabecular cartilage. Whether th e short band
of cartilage is of trabecular origin, or not, I can n o t positively tell, b u t it would seem as if the
trabecular cartilage could n o t extend posteriorly, on either side, beyond th e hind end of the
thickened ventral edge of th e alisphenoid cartilage. This being th e case, th e short band of cartilage
would represent th e anterior end of th e parachordal cartilage, and as such I consider it; th e hypophysis
then lying between th e anterior ends of the parachordal cartilages. Parker shows this p a rt
of the chondrocranium of Lepidosteus somewhat different from what I find it, and he considers th e
cartilage of th is region as of trabecular origin; b u t he also considers th e basipterygoid process as
of trabecular origin, and th a t cartilage, being a process of th e prootic cartilage, must certainly be of
post-trabecular origin.
The basipterygoid process of Lepidosteus, it may here be stated, has so closely the position
and th e relations to th e nerves and blood vessels of th e region th a t th e basipterygoid process of
Lacerta has (Gaupp, ’00, p. 537), th a t it must be th e homologue of th a t process. In Amia, it is
apparently represented in th e little cartilaginous process th a t is perforated b y the efferent pseudo-
branchial arte ry (Allis, ’97a), and th a t rises from th e lateral edge of what is apparently the hind
end of th e fused trabeculae. In most teleosts th e process seems wholly wanting. .
Pa rk e i’s alisphenoid bone is thus, as I find it, even in 55 mm specimens, simply a p a rt of the
ascending process of th e parasphenoid, and I am unable to explain how Parker could have found it,
separate and independent, not only in a 2 inch (50 mm) b u t also in a 4 inch (100 mm) specimen.
Parker furthermore states th a t his alisphenoid is an endosteal bone. In my 55 mm and 80 mm
embryos th e corresponding basipterygoid process of the parasphenoid is, in its anterior portion,
surrounded by dense tissue th e character and origin of which I am unable to determine, n o t being
sufficiently versed in th e subject; b u t it would seem to result, in part, from th e breaking down of the
superficial layers of th e cartilage against which th e bone lies. In the 19 mm and 25 mm specimens this
dense tissue is already being developed, b u t a t these ages th e tissue lies almost entirely between the
bone and th e cartilage, and i t m ay accordingly be wholly of perichondrial origin. Whatever its origin,
this p a rt of th e parasphenoid certainly has relations to the underlying cartilage somewhat different
from those of th e other portions of th e bone, and it would seem to be a typical case of a dermal bone
in process of acquiring primary relations to an underlying cartilage. I t is, however, to be noted
th a t perichondrial bone has nowhere else appeared, in the earliest of th e stages examined, and th a t
when it does appear it is not imbedded in dense formative tissues, as th e bone here in question is.
In th e ad u lt this p a rt of the ascending process of the parasphenoid certainly has much the appearance
of perichondrial bone; b u t it runs insensibly into the posterior portion of the process, where both
plates of th e V-shaped portion of th e bone are certainly of ectosteal origin, for they both extend
beyond th e dorso-lateral edge of the cartilage they enclose, and there overlap, superficially, portions
of th e inner and outer surfaces of the ventro-mesial edge of the prootic bone. But, whatever its
origin, this p a rt of th e parasphenoid is certainly n o t th e alisphenoid, for th a t bone is found elsewhere,
in its proper place, as a wholly independent ossification.
In th e adult, on th e anterior edge of th e basipterygoid portion of the ascending process of the
parasphenoid, there is a tit-like process which projects toward and sometimes even abuts firmly
against th e lateral surface of th e body of th e parasphenoid slightly anterior to th e base of its ascending
process. This little process lies in a horizontal position, a t right angles to th e axis of the parasphenoid,
and between it and th e anterior edge of th e basal portion of th e ascending process there is a more
or less completely closed opening which transmits the efferent pseudobranchial artery. The anterior
edge of th e tit-like process is straight and forms p a rt of the articular surface for th e metapterygoid,
the remainder of th a t articular surface being formed b y the straight anterior edge of the basipterygoid
process and a corresponding edge of th a t p a rt of the prootic cartilage th a t lies dorso-lateral to the
process. This little tit-like process is thus a mesial growth of th e anterior end of th e V-shaped p a rt
of th e bone of embryos, and it is to be remarked th a t, although i t may ab u t firmly against the body
of the parasphenoid, I have never found it fused with th a t bone. I t is not. shown in any of Parker’s
figures, b u t the general arrangement of the parts can be readily understood by reference to those figures.
Between the prootic bone and the hind edge of the external plate of the ascending process
of th e parasphenoid, there is an opening which leads into a short canal between the parasphenoid
and th e overlying cartilage of the basis cranii, th e opening thus having exactly the position of the
internal carotid foramen of Amia and teleosts, and unquestionably being the homologue of th a t
foramen. In Lepidosteus, however, this foramen transmits the common carotid, which artery,
immediately within th e foramen, separates into its external and internal branches. The external
carotid, turning upward, traverses a foramen th a t perforates the ventro-mesial edge of th e prootic,
b u t lies pa rtly in th a t bone and p a rtly in th e cartilage th a t bounds it. The arte ry then runs upward
Zoologica. Heft 57.