DEVELOPMENT OF THE SKULL IN THE PIG. 30. 
part of the rod, is continuous with the long descending part of the arch (see Plate XXX. 
fig. 9, st.h.); it is the head of the stylohyal. Here we see that the second postoral 
arch grafts its capitular portion on to the auditory segment, and splits its tubercular 
portion into two new condyles, one of which, covered by the squamosal on the outside, 
articulates with the tegmen tympani; whilst the other, retreating very sensibly, 
coalesces with the ear-sac further backwards and downwards, close in front of the exit 
of the portio dura nerve. In the figure these parts are continuous; but the continuity 
is kept up at present by new cells, and these younger cells are all soft indifferent tissue 
as yet; their morphological differentiation will be explained in the next stage*. 
Behindthe stylohyal and some distance outside the promontory (pr.), the portio 
dura nerve (7”) is seen in section, an excellent land-mark for the stylohyal; further 
backward the compound 8th nerve (8%, 8’) is seen in the “foramen lacerum posterius” 
(f-l.p.); the hypoglossal (9) is enclosed in the upgrowing exoccipital cartilage (Plate 
MX. figs. 3; 9; ¢.0.). 
The relation of the auditory sac to the exoccipital (¢.0) is shown in fig. 7; the whole 
arch of the horizontal canal is seen shining through the cartilage, and its ampulla is 
obscured by the fibres of the portio mollis nerve (7’); the Gasseran ganglion, and the 
compound 8th nerve are also severed (5, 8%, 8’). 
Third Stage-—Embryo Pig, Ly inch in length. 
Those metamorphic processes which were rapidly proceeding in the last stage have 
become very complete in this, where the embryo is one third longer: this stage must be 
copiously illustrated and described at length, as it is the best stepping-stone between the 
early simple and the later transformed conditions. The sections now to be described 
are a series from the end of the snout to the occipital region. Parallel to each other, 
yet they do not .keep the same vertical relation to the embryonic head, but become 
almost horizontal sections of the occipital region. the whole head at this stage is about 
equal in size to a horse-bean. 
The first of these slices is through the end of the snout (Plate XXXI. fig. 1), and 
shows the coalescence of the alinasal cartilages with the backwardly bent trabecular 
cornua (al.n., ¢.tr.). The next (fig. 2) is through the foremost part of the septum nasi 
(s.z.) and valvular fold of the nostril—rudiment of alinasal turbinal (q/. tb.): a more 
enlarged view of the lower half of the septum (fig. 2%) shows the large and massive 
trabecular cornua, and the prenasal part of the trabecular commissure between them. 
In the next (figs. 3 & 3") the cornua are now seen to be retral, for here they are 
becoming separate from the ‘ prenasal ;” still the base of the septum nasi as well as their 
* Thave studied the development of this interhyal tract in the Batrachia Anura and Ophidia, where it 
never even chondrifies ; in the Eel (Anguilla), where it is very small and indistinct as cartilage, and fades into 
a mere ligament; in the Osseous Fish (Salmo salar) and the Ganoid (Accipenser sturio), where it becomes an 
ossified rod of cartilage; and in the embryo of Linota cannabina, where it chondrifies after a time and fuses 
together again the incus and stylo-hyal. 
