THE BRAIN 771 
The ninth or glosso-pharyngeal, the tenth or vagus, and the eleventh or spinal 
accessory nerves are connected by a linear series of roots with the lateral aspect of 
the ventral surface of the medulla. The spinal part of the accessory nerve comes 
forward along the edge of the medulla to join its medullary root. 
The twelfth or hypoglossal nerve arises from the posterior part of the medulla 
along the lateral edge of the pyramid. 
The parts that are visible when the brain is viewed from above are the cerebral 
hemispheres, the cerebellum, and part of the medulla oblongata. The cerebral 
hemispheres (Hemisphzeria cerebri) form an ovoid mass, and are separated from 
each other by the median longitudinal fissure (Fissura longitudinalis cerebri), 
Longitudinal fissure 
' 
SSS 5$= Olfactory bulb 
— Olfactory tract 
_-——- Medial stria 
—-— Lateral stria 
—~ Trigonum olfactorium 
Piriform lobe ~ — Fossa lateralis 
Pitwitary body — +- Cerebral peduncle 
Oculomotor nerve — 
- Tractus ped. transversus 
sensory root ~_ ¥— Interpeduncular fossa 
Trigeminal { 
ES 
NET VE | > aa 
motor root ——— = SoG Seah Pons 
Cerebellum ~ ae aS _——-—— Corpus trapezoideum 
. a 
Tuberculum faciale _—_———— ne geet 8 Pyramid 
Glosso-pharyngeal nerve : 
Vagus nerve : ee (ls eee Medulla oblongata 
Accessory nerve (medullary root) 
~~~ Chorioid plexus of fourth 
ventricle 
Hypoglossal nerve Z Sl .as SSS Median fissure and de- 
cussation of pyramids 
Accessory nerve (spinal root) * 
— Spinal cord 
Fic. 630.—Line Drawine or Base or Brain OF Horse. (Key To Fic. 629.) 
VI, Abducent nerve; VII, facial nerve; VIII, acoustic nerve. 
in which the falx cerebri is situated. Their surfaces are marked by thick ridges, 
| the gyri cerebri, separated by sulci. The upturned ends of the olfactory bulbs 
are seen in front of the frontal poles of the hemispheres. The occipital poles of 
the hemispheres overlie the anterior part of the cerebellum, from which they are 
separated by the transverse fissure (Fissura transversa cerebri) and the tentorium 
cerebelli contained init. The cerebellum is a much smaller rounded mass which con- 
ceals the greater part of the medulla oblongata. Its surface is divided into a middle 
lobe, the vermis cerebelli, and two lateral hemispheres (Hemispheeria cerebelli). It 
is marked by numerous gyri and narrow sulci which have in general a transverse direc- 
tion. The posterior third of the medulla oblongata is not covered by the cerebellum. 
The brain is developed from the expanded cephalic part of the neural tube of the embryo. 
The process comprises a series of thickenings, flexures, and unequal growth and expansion of 
