DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
175 
face ; the plate passes directly into the cartilage of the capsule on the left side. 
There the vestibule (vb.) is laid open and the horizontal canal ( h.s.c .) is exposed. 
2 3 rd Section (Plate 24, fig. 13). — This is only a little more than half the floor of 
the skull. The supra-auditory cartilage ( s.a.c.) is now passing into the supraoccipital, 
and is again free from the capsule. The horizontal canal (h.s.c.) is cut across its arch, 
the posterior canal ( p.s.c.) through its ampulla, and the anterior canal (a.s.c.), above. 
The large space between the capsule and the basal plate allows the 9th and 10 th 
nerves (IX., X.) to pass, and the large size, and the thick edges of the basal plate 
(b.o.) is due to the fact that the condyles are cut across. The notochord ( n.c .) is 
now directly beneath the basilar artery (b.a.); it is seen again in the attached wedge 
of the axis (ax.) ; the condyles of the atlas (at.) are also seen. 
24 th Section (Plate 24, fig. 13).—The basilar plate and condyles (oc.c.) are cut 
across in this section in the fore part of the foramen magnum. The roof-cartilage 
(s.a.c.) lies upon the auditory capsule. This latter shows inside it the hinder part of 
the horizontal canal, and the neck of the posterior canal (p.s.c.) close to the ampulla. 
In this, as in the last, the cartilage is very solid above and behind the canals. 
The 1 st, 2 nd,and 3rd vertebrae (at.,ax., and below it,a small nucleus),are partly shown. 
Fifth Stage.—Dissection of the lower face and throat of an embryo Mole ; 1 inch long. 
There is very little difference between these parts in an embryo an inch long and 
the same in one four-fifths of an inch (Plate 28, figs. 3 and 2 ). But in the larger 
embryo I was able to get a side view of the stapes (st.). It is shown in the figure 
dislocated from the incus (i.), and thus the triangular form and the round hole are 
shown. The incus also has its discoid articular facet for the stapes turned towards the 
eye. The facial nerve (VII.) is seen in its canal, and in front of it the epihyal ( c.hy .)'“ 
is seen to be confluent with the auditory capsule (au.), but only connected with the 
ceratohyal (c.hy.) by ligamentous fibres. The extremely thick and soft membrana 
tympani (m.ty.) is just beginning to have an osseous deposit in its rim, and its fibres 
radiate from the front of the manubrium mallei (mb.). The distal ossification on 
Meckel’s cartilage (mJc.) is elongating, and the dentary bone (d.) is creeping up the 
coronoid and condyloid processes of the superficial cartilage (c.p., cd.p.). There is no 
malleal ectostosis, at present. 
Sixth Stage.—Dissection of lower face and throat in an embryo Mole; 13 - inch long. 
In an embryo a little more advanced than the last there are several things in the 
facial arches worthy of notice. The superficial mandible (Plate 28, fig. 4) has not 
only increased its bony matter, but the cartilage has become much more solid and in 
larger quantity ; the middle process ending in the condyle (cd.p.), especially, is a thick 
rounded mass ; the glenoid cartilage (gl.c.) is seen capping the condyle. The hypo- 
branchial element of the arch—the distal Meckelian ossification—is now larger, and 
* In the letters of reference the hinder c.liy. should have been e.hy. 
