DEVELOPMENT OF THE SKULL IN THE PIG. 



301 



{c.hy.) is cut through near its junction with the long stylohyal, and the " cornu major " 

 {br. 1) is shown in its whole extent on each side; whilst between we have the basal 

 piece (b.br.), not, truly, a basihyal, but answering to the first basibranchial of the Fish. 

 The larynx (Ix.) is below and behind them, and behind it is the oesophagus («.). 



Another section (Plate XXX. fig. 3), taken further back than the last, shows the sphe- 

 noidal, auditory, and occipital regions as seen from above. The differentiation of parts 

 has gone on very rapidly, whilst the embryo has merely become longer by one half, and 

 the difficulties in the way of interpretation are largely removed. 



In front the " anterior clinoid wall " [a.cl.) is seen to be symmetrically divided at the 

 mid line; this is the junction of the trabeculse at the end of their long commissure, in 

 front of the outbent blades which pass around the pituitary region. The pituitary cup 

 is deep, wide, narrow above, and has a crescentic form, the concavity of which looks 

 forwards. Between this actual cavity and the free ascending ends of the notochord and 

 investing mass there is a large amount of gelatinous tissue, through which the wavy 

 internal carotids [i.e.) pass, converging and again diverging. The gelatinous tract, the 

 base of the so-called " middle trabecula " (see Plate XXVIII. fig. 6, m.tr.), is widest close 

 to the ear-sacs, and narrows to the edge of the pituitary pit ; on each side of it is seen 

 a bulbous mass, the Gasserian ganglion (5). On each side of the extremity of the 

 notochord and investing mass are seen the well-defined ear-sacs, which are here cut 

 through in their cochlear region ; the coils are now well developed. On the left side 

 the section is behind and below that shown on the right, where the " malleus " or head 

 of the first postoral is cut through, the shaft of the second arch, and the " meatus 

 externus " and outer ear. Part of a similar section, taken lower down (fig. 4), displays 

 the orbito-sphenoids in section (with their upper part cut away); and where they have 

 coalesced with the trabecular commissure, there the optic nerves (2) are crossing. The 

 alisphenoids (al.s.) are sections seen in their whole extent, but not their connexion 

 with the basisphenoid, the notochordal region of which is displayed, backwards to 

 where the basioccipital territory begins. 



At a lower level closely packed cells are developing into cartilage, which will form 

 a secondary floor to the pituitary body, the seat of the " sella turcica ;" then the poste- 

 rior sphenoid will be morphologically complete. The connexion of the two great post- 

 oral bars with the auditory capsule will be better understood by two more sectional 

 views similar to the large figure (Plate XXX. fig. 3), but of more limited extent and 

 more highly magnified : all these figures are made from the antero-inferior aspect of the 

 up-tilted basis cranii, the sections, which in the nasal region were vertical (figs. 1 & 2), 

 being horizontal behind. Such a section (Plate XXX. fig. 6) through the outer ear or 

 concha [ca.) and head of the first postoral bar shows how curiously incurved this capitular 

 portion is, and how that its apex is developed into an orbicular part, like that on the 

 apex of the next bar. The shoulder, which articulates with the upper part of the 

 next bar, is very bulbous, and at the root of the neck a conical boss is sent outward ; 

 the shoulder is the head of the malleus, the boss is the process for attachment of the 



