188 
MR. W. K. PARKER OK THE STRUCTURE AKD 
Tenth Stage (continued).— The visceral arches. 
Notwithstanding the more specialised nature of the Mole, as compared with the 
Hedgehog, some things in it are much more like what is seen in the Metatheria than 
anything to be found in that larger and more normal Insectivore. 
In these large “ nestlings ” the three lobes of the lower jaw (Plate 28, fig. 7, c.p., 
cd.p., ag.p .) are still largely composed of cartilage. Meckel’s cartilage (ink.) is to a 
great extent lost in the general dentary ossification (cl), hut it is seen behind, wedged 
in between the condyloid and angular processes of the jaw. The ossicula are now 
largely ossified and the bony deposits forming the malleus (ml.) are exceedingly 
instructive and very Metatherian. Besides the ordinary ectosteal tract, which has set 
up endostosis in the head of the malleus, there is an almost distinct sjdint under the 
neck of the malleus, which is the true counterpart of the os angulare of the Ovipara. 
The manubrium (mb.) is mainly cartilaginous, but there is a fusiform epiphysis in the 
middle of this process ; this is very noteworthy ; for in Lepidosteous and in Amia the 
££ articulare ” is ossified by two centres ; and this is manifestly the additional centre 
cropping up once more.* 
The three most projecting parts of the incus (i.) are still unossified; the short crus 
(s.c.i) is very small. The stapes ( st .) is merely indicated in outline ; so also is the 
annulus; the epihyal ( e.hy .) is confluent with the auditory capsule (cm.) where 
the facial nerve (VIT.) emerges. A short ligament connects that second segment of 
the hyoid arch with the top of the subdivided ceratohyal (c.hy .); this is a gently curved 
rod, occupied by a shaft of bone for half its extent. The next segment (c.hy' .) is only 
two-thirds the length of the upper, and is one-third thicker; it is just beginning to 
ossify. So also is the still shorter and stouter hypobyal ( h.hy .) which fits obliquely 
on to the basi- and thyrohyals ( b.h.br ., t.hy.) ; these rods are ossifying, but the distal 
half of the paired rods is soft. The annulus (Plate 25, fig. 13, a.ty.) and the imperfect 
cartilaginous tube of the meatus (m.c.) show the normal type of the outer ear, with 
arrest of the concha ; it has four rudimentary rings. 
Eleventh Stage .— Young Mole; tiro-thircls grown. 
The side meiv ot the skull at this stage (Plate 27, fig. 4) is very similar to that of 
the last (fig. 3). I have, however, figured the squamosal, in situ, in this; the malar 
or jugal, is left out, here, for the better display of the fundus of the imperfect orbit. 
The length of the figures is nearly the same, those of the larger specimen being some¬ 
what larger, although they are magnified much less. 
The bones are much stronger and more polished, and the cartilage is rapidly 
disappearing; the snout (al.n.) is relatively slenderer. The imbrication of the 
* In toe Green Turtle tliere are two articular centres-: one the endosteal, developed late, and the 
other the ectosteal, developed early, and just like the other bony plates around it; these, however, are 
merely the two elements of one ossification. 
