692 
MR. T. W. BRIDGE ON THE OSTEOLOGY OF POLYODON FOLIUM. 
in Huxley’s figure,* are not paired dermo-etfimoids, corresponding to the paired 
endosteally formed centres which in that Teleostean represent the median ethmoid of 
other Fishes, it would appear that they must correspond to the paired ossifications 
marked 6 s in both Polyodon and Acipenser, the serial liomologues of the parietals 
and frontals. The bones marked 1 in the same figure apparently belong to the lateral 
series, and would probably represent the nasals of other Fishes. 
It may also be mentioned that the generalised medio-dorsal and supero-lateral cranial 
plates which invest the rostra of such Teleostean Fishes as Ostracion, Loncaria , &c., 
exhibit the same alternating arrangement which has been pointed out in Polyodon and 
Acipenser . 
The parasphenoid (Plate 55, figs. 2 and 3 ; Plate 56, fig. 4) is of great length, 
extending from a point just in front of the nasal capsules to a considerable distance 
beneath the coalesced anterior vertebrae. The postcranial part of the bone expands 
and bifurcates in order to allow the efferent branchial vessels to reach the anterior 
part of the dorsal aorta, and the two slightly divergent arms receive between them 
the anterior part of the massive notochord and the commencement of the haemal canal. 
The cranial part of the bone is slightly convex below and concave above where it is 
applied to the cartilage of the basis cranii. After slightly expanding between the 
nasal sacs the parasphenoid contracts in the orbital region, and again expanding 
beneath the auditory capsules, sends off on each side a short triangular basi-temporal 
wing ( b.tp .) which passes upwards and outwards between the foramina for the exit of 
the palatine and spiracular divisions of the seventh nerve, closely applied to the car- 
tilage that forms the thin outer wall of the short Facial canal which traverses the 
outer wall of the periotic capsule between those foramina, and terminates above in a 
point just in front of the lower end of the groove for the head of the hyomandibular. 
At the base of this process the parasphenoid gives off a second and smaller process, 
which is directed outward and backwards as in Amici, and to the angle between 
the two the pharyngo -branchial of the first branchial arch is attached. (Plate 55, 
fig. 3, b.tp.) 
Just in front of its bifurcation the lower surface of the parasphenoid is marked by 
two osseous knobs, and the lateral margins of its anterior moiety are slightly over- 
lapped by the adjacent cartilage. In front of the parasphenoid, and anterior to 
the internasal area, there is a pair of splints (fig. 2, vo.) which appear to represent 
the vomers ; and wedged in between their anterior ends there is a second mesial 
splint (p l ) extending backwards nearly to the anterior end of the parasphenoid. If 
the paired splints are correctly to be regarded as vomers, then this azygous splint 
would appear to be the liomologue of the anterior parasphenoid described by Parker! 
as existing in Rana pipiens. 
In front of the mesial splint (p~) there is a third median splint (pr‘) continuing the 
* 4 The Anatomy of Vertebrated Animals,’ p. 154, fig. 46. 
f “ Structure and Development of the Skull of the Common Frog,” Phil, Trans., Vol. 161, p. 193, 1871. 
