DEVELOPMENT OF THE SKULL IN THE PIG. 315 
within, above, and below (figs. 1, 2, 5, 6, @u.), but as a mass they are not much changed 
from the last stage. 
Tn the sectional view (fig. 5) the Eustachian tube (ev.) is seen below the basisphenoid 
(.s.); below the soft palate the ceratohyal (¢.hy.) is cut through, and along the inside 
of the lower jaw the primary mandible is seen. ‘This is better shown when dissected 
out (fig. 7); and now its malleal end is ossified (this part is cut through in fig. 1), whilst, 
below, the Meckelian commissure is sévered, the bars uniting along their anterior 
fourth. I can only find one osseous centre here in the mandible, the dentary (d.); this 
is found in the rapidly chondrifying nidus, which, like a huge “ inferior labial,” obliquely 
overlaps the primary mandible; in Man, according to CALLENDER, there is an osseous 
centre at the chin in MucKEL’s cartilage, and a second splint (splenial) on the inner face 
of the dentary (see Phil. Trans. 1869, Plate xu. figs. 6 & 7, p. 170). 
A few of the many sections prepared of this stage will now be described, and they 
will thoroughly explain the structure of the parts which have above been described 
mainly from dissections. 
The first is through the snout (Plate XXXIV. fig. 8), and shows the arched cartilages, 
united together in front, which were formed by fusion of the ale nasi with the overbent 
trabecular horns. 
The second (Plate XXXIV. fig. 9) is through the ale nasi (a/.7.), fore part of septum 
(s.n.), alinasal turbinal (a/.tb.); and the masses with trilobate outline below are the 
recurrent trabecular horns (7¢.¢.). 
The third section (Plate XXXIV. fig. 10) shows a curious triradiate cartilage separated 
from the “ale nasi;” this is the “ appendix” (a.al.n.); here the trabecular cornua are 
becoming slenderer. 
The fourth (Plate XXXIV. fig. 11) shows the same parts further back; here the 
recurrent process has become a smallish band lying flat on each side of the base of 
the septum, which is now becoming high, but has not commenced the inferior turbinal 
fold. The four-winged section, on each side, below the septum and recurrent cartilages 
is the severed premaxillary (pa., see also fig 2). 
The fifth (Plate XXXIV. fig. 12) is through the middle of the inferior turbinal (7.¢0.) ; 
the pedate section here shows the upper limb coiled on itself, but not the lower at present. 
The recurrent lamin of the trabecular horns are running even past this point backwards ; 
they are here vertical, and in close relation with the nidus of the scoop-shaped vomer (v.)*. 
In this section the outer stratum of granular tissue overlying the nasal canals is now ossi- 
fied as the nasal bones (z.), and the mass of tissue overlying the pterygo-palatine bar has 
become the maxillary (m.), with its deep dental groove and pulps and its palatine plate. 
The stath (Plate XX XIII. fig. 4) section is through the solid anterior third of the 
* The relation of these recurrent developments of the trabecular horns to the splints that belong to the first 
facial arch is of intense interest; I am working out this subject in various groups; it is most complicated in 
Passerine Birds, ‘ Hgithognathe”’ (H.). They are evidently formed by the fusion of a “labial” with cach 
5] 
trabecular horn. If we add to this the “appendix ala nasi’ and the secondary mandible, we get thirce pairs 
of suctorial cartilages in an ordinary Mammal. 
272 
