THE SKELETON 



37 



Per 



between the premaxilla and maxilla of either side. Behind the nasals 

 and maxillae, the anterior part of the brain-case is formed by the 

 large paired frontals (Figs. 6, 7, Fr), 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- 



1 /TT' *7 <y \ ( '~ Side view of skull of Cape Jumping Hare (Pedetes 



OSal(rig. <,0</; lorms ca/er). x?. PMx, Premaxilla; MX, maxilla; Ma, jugal or 



the lateral Wall of malar ; Fr, frontal ; L, lachrymal ; Pa, parietal ; Na, nasal ; 



the hinder part Of S9> S( l uamosal J r 2/> tympanic ; ExO, exoccipital ; AS, alisphen- 



oid ; OS, orbitosphenoid ; Per, mastoid bulla. 



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 affinity. 

 The relative position occupied by the orbito- and alisphenoid is 

 sufficiently 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 



