428 GEACE A. WELLS 



This figure shows well the trough of the rostrum and its me- 

 dian keel. Ventral to the notch at the anterior end of the 

 brain case is an opening through to the ventral side of the cra- 

 nium, just medial to the nasal capsule. This is the fenestra, 

 the basal communication of Gegenbaur, mentioned in the ac- 

 count of the ventral surface. Dorsal and posterior to this is 

 the opening leading into the nasal capsule, through which the 

 olfactory tract passes (o.n.c). 



Slight ridges in the internal cranial wall mark off the brain 

 cavity approximately into thirds. The most anterior of these 

 regions is that in which the prosencephalon lies and the only 

 foramen here is a small one in the postero-dorsal part of the 

 region for the passage of a blood vessel (6.), the relations of 

 which were not determined. The central region, the location 

 of mes- and metencephalon, corresponds in general with the 

 external orbit. At its lower anterior angle is the large optic 

 foramen (o.II). Just anterior to this is a slight thickening, the 

 presphenoid process (Praesphenoid Vorsprung) of Gegenbaur's 

 description. At the upper anterior angle of this region is the 

 small foramen for the trochlearis nerve (IV). In the posterior 

 part of this region, near the floor of the cranium, is the canal for 

 the entrance of a blood vessel into the orbit (b.). Just dorsal 

 to this is the foramen of the oculomotor nerve (o.m.). At 

 the base of the dorsum sellae, in the floor of the cranium, is the 

 foramen for the transbasal canal (tr.c.) and ventral to it, and 

 slightly anterior, is the canal for the internal carotid artery 

 (int.c). 



In the anterior part of the posterior region there are three 

 large foramina in a common depression (the acustico-trigemino- 

 facialis recess of Allis). The most anterior of these is the for- 

 amen trigemino-facialis (t.f.), the most posterior is that of the 

 glossopharyngeal (IX), while the middle foramen is for the 

 auditory nerve (VIII). Gegenbaur called the most posterior 

 of these the auditory foramen, and the middle one, the facial, 

 but probing from the basal opening of the ninth shows that it 

 leaves the brain case through the most posterior of the three 



