114 MR. W. K. PARKER ON THE STRUCTURE AND 
ing a remarkable structure right and left of the axial crest, which is hollow between 
these two sessile berries of cartilage, and then thickens as it passes into the presphe- 
noidal region (p.s.). 
We must cross over into the territory of another group of the “ Amniota ’ to get 
an explanation of these parts, which appear to be rather for ornament than use, but 
which are really most important in their morphological signification. 
In the chondrocranium of the Crocodile and Alligator (see Trans. Zool. Soc., vol. xi., 
plates 63-67, and especially plate 67, fig. 1, i.tv., ¢.tr.) we have the explanation of 
this right and left berry-shaped swelling of the hind part of the ethmoidal region. 
They are the swollen ends of the paired trabeculze 
familiar to us in the Ichthyopsida.* 
the “cornua trabecule,” so 
A large unciform lobe of the orbitosphenoidal cartilage (0.s.) is seen lying upon the 
bony alisphenoid (q/.s.), but it is now two-thirds its own length from the front edge of 
the large superauditory (or pterotic) cartilage (s.a.c.), with which it was once continuous. 
The hind margin of the still large orbitosphenoid is a great semicircular notch, the 
fore margin is wavy, up to the rounded front and outer margin. The first and largest 
rounded notch of the orbitosphenoid fits against the berry-like cornu trabeculz (e.t7.), 
and the inner angle of the bone is separated from the same part of the other side by 
cartilage, the hindmost part of the perpendicular ethmoid (p.e.). Nearly in the 
middle of the inner margin of the bony part the oblique optic passage (IT.) is seen well 
margined by bone behind (see also fig. 1), but in this aspect this margin of bone is 
pressed upon by a mass of cartilage. Between the two bony tracts—orbitosphenoids 
(0.s.)—there is a short, thickish wedge of bone with notched sides ; this is the presphe- 
noid (p.s.), it is doubtfully independent, but is well marked off by a right and left 
groove, t 
The cartilaginous tract between the pre- and basisphenoidal ossifications is also 
elevated into a sort of double berry ; here with no stem between. Here we have the 
trabeculee behind the intertrabecula, with the thickening at their origin, showing here 
most on the upper side, whereas this is seen most on the lower in the Crocodilia (op. 
cit., Plate 65, figs. 1-8). The large bony ale (al.s.) lie down low and are well scooped ; 
they have a sharp raised ridge on their inside, and this is separated from the now 
confluent basisphenoid by a groove which is open at both ends; in the hinder space 
the internal carotid artery (7.c.) enters, and then runs along the groove. In front, the 
basisphenoid projects between the roots of the trabecule ; behind, it is notched thrice 
* The reader is also referred to the sections of the skull of the embryo Turtle (Chelone viridis) 
(‘ Challenger Reports,’ Zool., vol. i., plate 5, especially fig. 7,7.tr., tr.). Tf these figures be compared with 
those of the like sections of the skull of the embryo of Struthio camelus (Phil. Trans., 1866, 
Plate 10, figs. 2-5, s.n.), and of the skull of the Chick (Phil. Trans., 1869, Plate 81, fig. 6, s.n., and 
ibid., Plate 83, fig. 4, s.v.l.), the meaning of these things will be evident. 
{ The presphenoid is very rarely an independent ossification ; it attains to that special condition most 
perfectly in the Marsupials and Rodents; but in that remarkable Insectivore, Rhyncocyon, the pre- 
sphenoid has evidently had its own longitudinal centre of ossification. 
