DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
81 
is arched outwards, and runs from end to end of the bone, its hind part being continued 
into the inner fork of the bone. From this ridge a scooped plate runs inwards as a 
palatine flange to the main bone ; its outline, on the inside, is symmetrical with that of 
the alveolar ridge. The right aiid left lanceolate palatine plates are separated by a 
space nearly their own individual width ; the first third of this space is taken up by 
the palatine processes of the premaxillaries and the front paired vomers, the hinder 
two-thirds is occupied by the vomer, proper ( v .), the outer edges of which rest upon the 
corresponding palatine plates of the maxillaries. The vomer is split in front, keeled all 
along, and somewhat trilobate behind; it is a stout, shortish bone. The nasal capsules 
are seen inside and around these bones—side, septum, and terminal recesses (al.s.p., 
al.e.) ; the septum is first seen where it begins to run over the fore part of the vomer, 
and the proper olfactory region, after swelling outwards beyond the maxillaries, runs 
inwards over the sharp forks of those bones, to end right and left of the presphenoidal 
region (p.s.). 
As far as the maxillaries are concerned, this skull is now perfectly ‘ 4 schizognathous; ” 
so it is as regards the palatines ( pa .), which are in a very primitive, quasi-reptilian 
condition. Each bone is falcate, and arched inwards ; it is thicker forwards than 
behind, is a sharp wedge in front, binding obliquely on to the inside of the inner 
sharp process of the maxillary, whilst, behind, it runs outwards as a fine point of bone, 
binding over the pterygoid ( pg .). Behind the vomer ( v .), the palatines are, at their 
nearest, nearly their own width apart, whilst, further back, they expose the whole 
width of the basicranial beam. 
The palatal series is completed by the pterygoids (pg.) ; these bones are only two- 
thirds the length of the palatines, of the same thickness, on the whole, and are wider 
apart, for at their middle they elbow out, like two pieces of “ knee-timber.” The 
fore end of each bone is sharp, and runs obliquely inside the palatine, the hind 
converging part is rounded, and is capped by a truly cartilaginous remnant of its 
mother-tissue. This cartilaginous hamular process is common in the embryos of low 
Eutheria. It is a slight re-appearance of the old “ptery go-quad rate” of the Ichthyopsida. 
The rest of the superficial bones seen in this view are the frontals (f), and the 
squamosals (sq.) ; the former are turned in under the suborbital ridge, and over the 
orbit, and the latter are applied to the endocranium opposite the pterygoids. The 
frontals are very partial, however, in this region, and only partially invest the arrested 
orbitosphenoids ( 0 . 5 .). Behind these endo- and exo-skeletal laminae there is a large 
lateral fontanelle, which takes up most of the posterior region of the orbital space 
(see also fig. 3). The squamosals are distinguishable from those of a Chick by the 
presence of a small, flatfish, pyriform tract of cartilage attached to their jugal process ; 
in the Chick this process serves for muscular attachment merely ; here, in this low 
Mammal, we have the “ glenoid ” facet for the special Mammalian mandible, at its 
lowest state of development. 
The floor and sides of the chondrocranium are largely seen in this view; I have 
MDCCCLXXXV. 
M 
