24 THE SALAMANDER 



anterior portion of the space between the nasal capsules is thus open 

 ventrally. It is called the cavum internasale (ca.in.) and houses the 

 intermaxillary gland. The posterior wall of the cavum internasale is 

 formed by the septum internasale^ which connects the nasal capsules 

 posteriorly. It forms the cartilaginous partition between the cavum 

 cranii and the cavum internasale and bounds the mesial borders of the 

 jenestrae olfactoriae. The tectum internasale (c.t.in.) unites the capsules 

 dorsally and thus forms a roof to the cavum internasale. It is pro- 

 longed anteriorly in the middle line to a short beak, the rostrum 

 ■prenasale (Parker) (c.r.). 



{h) The next region of the primary skull is the Orbito-temporal. 

 It consists of a pair of vertical lamellae joining the olfactory capsules 

 to the otic capsules, and forming the sides of the brain-case, so that 

 they separate the cavum cranii from the orbits. They are perforated 

 by two foramina of which the larger is the for. opticum (fo.op.) and 

 the other, immediately posterior to it, is the/or. oculomotorium (fo.oc). 

 The optic foramen would perhaps be better termed the optic fenestra^ 

 since its diameter is much greater than the optic nerve, and it is 

 largely closed by membrane. In the adult the part of each lamella 

 anterior to the vertical diameter of the for. oculomotorium becomes 

 ossified, and the resulting bone is most usually termed the orhito- 

 sphenoid (o.o-s.), although Broom holds that it is the homologue of 

 the Mammalian pre-sphenoid and Noble refers to it as the spheneth- 

 moid. The older and more widely used name is retained here. 



{c) The Otic Capsules. The membranous labyrinth of the audi- 

 tory capsule is entirely enclosed by the primary skeleton which, in the 

 adult, ossifies completely with the exception of the operculum. The 

 capsules are relatively large and somewhat flattened dorso-ventrally, 

 especially towards the posterior region. On the dorsal surface may 

 be seen the convex ridges marking the position of the semicircular 

 canals of the labyrinth. The lateral end of the ridge covering the 

 horizontal canal is somewhat roughened where it meets the squa- 

 mosal and it is often referred to as the crista muscularis (cr.m.) from 

 the fact that certain spino-occipital muscles are attached thereto. 

 The ventral and anterior surfaces of the capsule are much smoother. 

 On the postero-lateral face, and directed somewhat ventrally, is an 

 oval opening in the capsule — the. fenestra vestibuli. The fenestra is 

 closed by a tough fibrous membrane, to the outer surface of which 

 is attached the operculum (cop.). The operculum is a heavy plate of 

 cartilage, strongly convex on its external surface and slightly concave 

 internally, so that in transverse section it appears as a thick crescent. 

 The M. opercularis attaches this element to the suprascapula. The 



