THE SKELETON 37 
between the premaxilla and maxilla of either side. Behind the nasals 
and maxille, the anterior part of the brain-case is formed by the 
large paired frontals (Figs. 6, 7, /r), behind which are the parietals, 
which may be of still 
larger size, and form 
the greater part of 
the brain-case. <A 
median interparietal 
ossification (Fig. 6, 
IP) may divide the 
parietals posteriorly, 
and is itself articu- 
lated with the supra- 
occipital, to the lat- 
eral borders of which 
the parietals are also 
joined. The squam- 
ees a Fic, 7.—Side view of skull of Cape Jumping Hare (Pedetes 
osal (Fig. ‘y Sq) forms caer). xX}. PMx, Premaxilla; Mz, maxilla; Ma, jugal or 
the lateral wall of malar; Fr, frontal; 1, lachrymal; Pa, parietal; Na, nasal; 
Sq, squamosal; 7'y, tympanic ; x0, exoccipital ; AS, alisphen- 
oid; OS, orbitosphenoid ; Per, mastoid bulla. 
the hinder part of 
the brain-case, and 
articulates superiorly with the parietal, and posteriorly with the 
exoccipital. The glenoid cavity (Fig. 8), for the reception of the 
articular condyle of the mandible, is formed by the inferior portion 
of the squamosal, at the point where it gives off the zygomatic 
process to form the hinder portion of the zygomatic arch. The 
middle portion of that arch is formed by the jugal, or malar bone 
(Fig. 7, Ma), which articulates posteriorly with the zygomatic process 
of the squamosal, and anteriorly with the maxilla. The jugal (as 
in Fig. 7) may also articulate with a small bone situated on the 
anterior border of the orbit known as the lachrymal. It is im- 
portant to observe that the zygomatic or temporal arch is a 
squamoso-maxillary one, and that an arcade thus composed is found 
elsewhere only among the extinct Anomodont reptiles, which have 
already been mentioned as showing signs of mammalian aflinity. 
The relative position occupied by the orbito- and alisphenoid is 
sufliciently indicated in Fig. 7 
Wedged in between the squamosal and the bones of the occipital 
and basisphenoidal region are the bones connected with the organ 
of hearing, known as the periotic and tympanic. The position of 
the periotic, which encloses the labyrinth or essential organ of 
hearing, is shown in Fig. 6. The periotic is divided into a very 
dense antero-internal moiety known as the petrosal, and a postero- 
external or mastoid portion (Fig. 8), which appears on the outer wall 
of the brain-case. The tympanic is produced horizontally outwards 
to form the external auditory meatus or tube of the ear, while the 
