DEVELOPMENT OF THE SKULL IX THE PIG. 



309 



coalesces with the neck of the projecting stapes (Plate XXXVI. figs. 2 & 3, i.hy.,st.\ and 

 is half lost, at last, in the tendon of the "stapedius" muscle. The " cornvi minor " {c.hy.) 

 of Man is here seen (Plate XXX. fig. 9, c.hy.) below, articulating with the keystone of 

 the arrested third postoral. This lesser horn answers to the " hypohyal " (P.) of the 

 Osseous Fish. The twenty-second section, a front view (Plate XXXIII. fig. 1), is through 

 the three semicircular canals ; the anterior canal (its arch) is above, near the superocci- 

 pital cartilage («.sc., s.o.), whilst the horizontal canal (h.s.c.) is laid bare at its crown 

 and where its non-ampullar end enters the vestibule (vb.). The posterior canal has the 

 base of its ampulla laid open, and half the arch is seen shining through the cartilage ; 

 the lateral cerebellar recess [l.c.r.) is seen above the aqueductus vestibuli (aq.v.}. 

 The space between the auditory mass and the basi- and exoccipitals is the posterior 

 foramen lacerum {f.l.p. ; see also fig. 3) ; the basilar artery lies on the basioccipital, 

 and the notochord is within it [h.o., h.a., nc). 



From a series of sections taken horizontally in the nasal region, but which were cut 

 through the investing mass at a right angle, or nearly so, I have selected two as of most 

 importance in this demonstration. The first of these (Plate XXXII. fig. 9) is a front view, 

 and shows the left mandibular rod coming forwards and downwards, its manubrium being 

 buried in the tissue behind. The portio mollis (7*) is seen lying at the entrance of 

 the meatus internus. The anterior (superior) canal (a.s.c.) is cut through near its 

 ampulla, and the cochlea (cL) is divided at right angles to the plane of its coils. 



On the other side (left of the figure, right side of the head) the portio mollis (7^) 

 is seen streaming into the labyrinth, and the portio dura (7") is cut through close to 

 the tegmen tympani (t.ty.). The crown of the anterior canal is here cut through, 

 and the horizontal canal near its ampulla ; here the " tegmen " is seen at its high 

 anterior part, and the " short crus " of the incus lies in front of its descending portion, 

 where the overlying horizontal canal dips before it turns inwards to enter the vestibule. 

 The " long crus " of the incus (/.) is shown hooking upwards, and expanding into its 

 orbicular portion on the stapes (s^.), the apex of which has been cut away, exposing 

 the hole. The head of the stylohyal {st.h.) is cut through, and in the angle between 

 it and the long crus there is a large pisiform " interhyal" (i.h.y.). The basioccipital has an 

 irregularly pentagonal section, shows the notochord in its centre, and is very distinct 

 from the auditory mass : this distinction is very clear and persistent in the Mammalia. 



The plane from which the last section was taken being sliced again, yielded what I 

 have depicted in fig. 10 : this is a back view, and the left side of the figure corresponds 

 to the left side of the head. On the right side the occipital arch (s.o.) appears almost 

 to its crown ; on the left its fore edge is just missed. 



The left side of this figure corresponds very nearly to the left of the last, but the razor 

 has passed close behind the auditory nerve and through the promontory, where its 

 cartilage passes as a narrow band between the fenestrse (/. ovalis and/, rotunda), a tract 

 which receives osseous matter from the " opisthotic " centre. Here the base of the 

 stapes is towards the eye, and half of it is seen through the cochlear wall (pro- 

 montory) : the rest is as in the last figure. 



