196 
ME. W. K. PAEKEE ON THE STETTCTUEE AND 
nective (c e) is wholly loosened from the prefrontal region and runs back into the severed 
quadrate angle, below which is articulated the short, thick Meckelian rod (p). But 
above the severed quadrato-pterygoid there is, not as in Narcine , two pairs of cartilages, 
but one lozenge-shaped piece (&), evidently the two “ metapterygoids ” in one. This 
marvellously metamorphosed mandibular arch is followed by a most massive hyoidean 
apparatus, the result of segmentation and overgrowth of the second postoral bar. The 
little “ suprahyomandibular” of the Frog is here represented by a thick rib of cartilage 
having an ectosteal sheath near its upper condyle (Muller, fig. 10, M', M, N ; Huxley, 
f, g ; Huxley and Hawkins, pi. 5. fig. 3 A ). The broad unossified part carries the “ oper- 
cular” behind, and, below, ends in a round condyle, which is tied to the cup on the top 
of the next segment. This shorter but equally massive piece is invested with- bone, 
and has articulating with it, behind, a nodule of cartilage ; this is above the middle, 
and separates the “ infrahyomandibular ’’ and “ symplectic” regions; it is the “stylo- 
hyal” (see the figs, in Owen’s Lect. Comp. Anat. vol. ii. p. 131, fig. 43, between Nos. 
28 & 40). To the stylo-hyal is articulated the shortish, partly ossified, interiorly 
segmented cerato-hyal. (Owen, ut supra, No. 40 ; Huxley and Hawkins’s Atlas, pi. 5. 
fig. 3 6 , lly). 
Here, in the Sturgeon, apparently for the first time, that segment is found in the 
second postoral bar which answers to the Mammalian “ incus its prototype is the Stur- 
geon’s “ suprahyomandibular.” 
5. With the Skull o/Lepidosiren. — Save for the addition of bony investing plates, the 
skull in this type answers very closely to that of the Chimeeroids (see Huxley, Elem. 
pp. 207-210, figs. 84, 85). There is the same filling-in of the gaping space between 
the first two bars by the “ pterygo-palatine connective and the piers of the first two post- 
orals are entirely confluent ; the Meckelian and hyoidean rods are similarly free. I find 
a pair of oval upper labials attached to a short azygous “ snout-cartilage” (“prenasal”). 
6. With the Skull of Teleostean Fishes. — As I hope to make the Teleostean my next 
subject, I shall merely refer to what Professor Huxley has done with regard to the 
structure of the skull in very young Gasterostei. In his earliest stage (Croon. Lect. 
p. 29, fig. 8, left-hand figure, and Elem. p. 185, fig. 72 A.) the trabeculae, investing mass, 
and auditory sacs have become confluent, the commissure, which is the foundation of 
the ethmoid, is complete, and from this conjoined part of the trabeculae there proceed 
a pair of short emarginate “ cornua trabeculae.” The first postoral bar (mandibular), 
instead of attaching its free, rounded, upper end to the trabeculae and investing mass, has 
retained its freedom, and has somewhat descended from the skull. 
The auditory sac has grown over the top of the second postoral ; and it has expanded 
into a pedate form above, to embrace the sac antero-externally . Meckel’s rod, not shown 
in this figure, has been differentiated from the quadrate end of the mandibular arch, which 
has sent forward a triangular pterygo-palatine “ connective,” the apex of which touches 
the prefrontal region of the “ trabecula.” 
Let this stage be compared with my third (Plate IV. fig. 7, and Plate X. fig. 13), and 
