DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
157 
the inner being the larger and uniting by a “ harmony suture ” with its fellow of the 
opposite side. The ascending part of the palatines is strong and has coalesced with the 
external pterygoid plates (e.pg.) on the outer side; they have not united with the 
pterygoids (pg.). The hind margin of the hard palate, formed by the palatines, which 
have not united with the maxillaries, is an elegant archway with a strong upper lintel 
over it, formed by a thick rib on each of the palate bones ; these ribs meet at the 
mid-line at a very obtuse angle. 
The elements of the basis cranii behind and below are fast coalescing with each 
other; the sutures of the hind skull, however (fig. 4), are most of them visible. 
The paroccipital processes ( p.oc.) are thickish and somewhat foliaceous ; they finish a 
semioval occipital plane, with its large convex obliquely pyriform condyles ( oc.c .). But 
in front of the occipital arch the mastoid processes (fig. 4, op.) project like wings and are 
there strongly sutured to the postglenoid process of the squamosal (sq.), which is 
pneumatic, and has its own foramen. There is a large foramen lacerum posterius 
for the 9th and 10th nerves, and a lesser foramen condyloideum for the 12th 
(fig. 1, XI.).* The ossified auditory capsule has already been described (6th Stage, 
Plate 20, fig. 4), but the posterior sphenoid, and the turbinal folds of the nasal 
labyrinth, with the interior sphenoid can be well studied in this scarcely adult stage, 
whilst the parts are still capable of being taken to pieces to a considerable degree. 
The posterior sphenoid shown in its upper aspect (Plate 20, fig. 6), is a large winged 
bone, with a ragged outline and a multiperforate surface. 
The large foramen ovale (V 3 .) is at the hinder and the middle third of each great 
wing ( al.s .) ; the 2nd and 1st branches of the 5th nerve pass with the lesser orbital 
nerves out of the sphenoidal fissure. 
The fore part of the bone does not fit itself to the hinder part of the anterior 
sphenoid (Plate 21, fig. 7, o.s., p.s.), except at the middle ; the pointed fore end of each 
large wing grows outside, free of the orbitosphenoid. The outer and hinder part of 
each wing is rounded, and this upper surface is broken; it is strongly grooved where 
the 2nd branch of the 5th escapes from the 3rd and runs forwards and inwards to 
the great fissure. The narrow front part of the basisphenoid lies some height above 
the wings, and the bone has several small perforations at this part. The hinder 
broad part of this bar is very gently hollowed for the pituitary body, and the post- 
clinoid wall ( p.cl .) is extremely low. 
The lower surface of the bone shows the greatest number of diagnostic marks of a 
typical Insectivorous skull. The inferior wings, external pterygoid processes (e.pg.), and 
pterygoid bones (pg.), are well developed and have a good fossa between them. The 
latter are distinct from the palatines, but have come away, in disarticulation, with the 
basisphenoid, having already become ancliylosed to it, above. Between these internal 
plates the bone is sharply grooved, but, behind, between the tympanic wings, the basi¬ 
sphenoid has a large cup-shaped recess which might have lodged some such body as 
* For XI. read XII. in this figm’e. 
