322 
ME. W. K. PARKER ON THE STRUCTURE AND 
and the anterior and posterior sphenoids, are now thoroughly hardened. The “ spheno- 
occipital synchondrosis ” is of small extent, very thin, and a scarcely thicker tract of 
cartilage remains between the posterior and anterior sphenoids ; yet these are each a 
single bone at this stage. The perpendicular ethmoid and septum nasi are still 
unossified ; but the inferior turbinals are almost completely, and the “ lateral masses ” 
partially, converted into endosteal bone. The cribriform plate is soft, and so is 
the snout (Plate XXXYI. fig. 1) ; but this latter is everywhere burrowed with vessels 
prior to hardening. 
Beneath the skull we see a most compact building together of the palatal, pterygoid, 
external pterygoid, and tympanic bony pieces ; the thick, clubbed “ hamular process ” of 
the internal pterygoid is fixed as an undersetter to the solid nut-like tympanic, and dints 
it as an inturned horn dints the frontal in certain varieties of the Cow ; this, however, 
is only a temporary state of things, and is quite recovered from in the lengthening head 
and face. 
Xo “ interparietals ” have been found, adding two bones to the growing superoccipital, 
as seen in Man ; this part, the superoccipital, is now a nearly vertical wall, the parietals 
finishing the roof above. The lower jaw is well ossified, and is now entirely free from 
the arrested primordial bar, Meckel’s cartilage. The three periotic centres have 
completely ossified the auditory mass, “ petrosal ” and “ mastoid ” (Plate XXXVI. fig. 2) ; 
and a small bilobate ossicle has appeared in the attached (confluent) head of the stylo- 
hyal ( st.Ti .). Further down another centre has appeared in the middle of the long rib- 
like bar, taking up nearly the middle third. The upper piece of bone (formed from 
two nuclei in the Lamb, and apparently also in the Pig) is called by Professor Flower* 
the “ tympano-hyal,” a term it may be well to retain. The rudimentary stylohyal 
of Man is ossified from the upper centre ; for “ a centre of ossification appears in the 
styloid cartilage, and extending upwards and downwards, gives rise to the pyramid and 
styloid process” (PIuxley, ‘Elem.’ p. 160). Hence it will be seen that the tympano- 
hyal and the upper styloid bone are identical ; both these bones are largely developed 
in the Osseous Fish, the so-called “ epi- and “ ceratohyals they occupy the great flat 
“cornu,” at the base of which the short ceratohyal proper, with its two bony centres, 
is articulated. The unciform ceratohyal (“ cornu minor ”) of the Pig is strongly attached 
by fibrous tissue to the transverse basal piece (Plate XXXVI. fig. 2, c.h.), now coalesced 
with its own rudimentary arch, the “cornua majora” of Man; these pieces are ossified 
proximally (fig. 2, th.h.), and these centres correspond with the first pair of hypo- 
branchials of the Osseous Fish, the median part answering to the first basibranchial. 
The “ stylo-mastoid foramen ” (fig. 2, s.m.f 1, 7“) is seen transmitting the portio dura 
nerve ; and this sends upwards and forwards the “ chorda tympani ” (7“'), to which is 
attached the smallest of the three “ ossa bullae ” ( o.b '.) ; the middle-sized piece is seen 
in front of the stylohyal (o.b".). The rest of the drum-walls being removed and 
the squamosal, the outer face of the periotic mass shows the three semicircular canals 
* In his valuable little work ‘ On the Osteology of the Mammalia,’ 1870, p. 173. 
