DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
149 
open space. The postglenoid part of the squamosal ( sq .) is short, the hind part of 
the squama, in the end of the temporal fossa, is perforated. The facial nerve 
(VII.) is figured, and also its chorda tympani branch (Vll a .), passing to the large 
inferior branch of the trigeminal (V 3 .). The 1st and 2nd branches of that nerve 
(V 1 ., V 2 .), are seen emerging from the sphenoidal fissure, the former re-entering the 
skull through the main orbital foramen, and the latter running forward through the 
great maxillary canal, and emerging through the supraorbital foramen. 
The optic nerve (II.) is seen between the forks of the trigeminal (V 1 ., V 3 .), emerging 
from its own foramen opticum. 
The investing bones, as seen from below (fig. 1), show the finishing of a very fine 
piece of architecture ; the hinder superficial pieces, the tympanies, were removed to 
display the proper cranial structures. This individual was just cutting its teeth ; the 
huge sockets for which are shown with but partially developed dissepiments. 
The premaxillaries have a large dentary part, and a small, short palatine process ; 
over this, however, the anterior paired vomer (v'.), is seen, which afterwards makes 
that process of the normal size. 
The maxillaries (mx.) are enormous, being gravid with many large teeth, and, as the 
palate is very wide between the tooth-rows, the concave palatine plates are of great 
extent. There is, here, as in many of the Edentata, a sign of some distinctness of 
the inner, from the submarginal, part of this bony roof. The inner part is wedged 
in between the rami of the premaxillary ( a.p.f. ) in front, and then an oblique ridge, 
running backwards, and a little inwards, up to the posterior palatine foramen, marks 
the inner part off from the outer. The outer part of the hard palate is a concave 
tract, forming a lanceolate flange to the internal alveolar wall. The hinder part of 
the alveolar tract is unfinished; the jugal process is short and sharp. 
The palatine bones {pa.) are very elegant, and quite Metatherian in their 
characters ; their palatal plates are sharp wedges, running forwards, together, between 
the palatal plates of the maxillaries. An irregular subreniform fontanelle is seen 
in each plate, near its middle, behind the thickening inside the posterior palatine 
foramen ( p-'pf )■ Each bone has a thick subarcuate margin, as the finishing, behind, 
of the palatal plate ; these ridges are turned a little forwards as well as outwards. 
Part of the suberanial tract of each bone is seen behind the hard palate, bounding 
the nasopalatine canal; this is clamped by the pterygoid ( pg .); outside this, the 
palatine bone spreads into a hooked wing, which bends round the front of the 
oblique, oval, small external pterygoid plate ( e.pg .). The distinct upper vertical tract 
of the palatine ends a little behind the anterior sphenoid (o.s.), then the wall is con¬ 
tinued a short distance further back by the pterygoids ( pg .), which are not distinct, 
now, but have already coalesced with the sides of the wide basisphenoid bone ( b.s .); 
the lower part is terete, and ends in a short, free hamular process, which has, now, 
used up all the cartilage. 
The tympanies are not given in this figure; they have been removed, with the 
ossicula auditus, to display the auditory region. 
