VAN 121: Veterinary Gross Anatomy-II (2+2)

BRAIN

• The brain is that part of the central nervous system which is situated in the cranial cavity. Its average weight is about 500 grams in the ox, 1.5 kg. in man, 750 grams in horse and 60 grams in dog.
• When the brain is seen from above, the parts that are visible are cerebral hemispheres, cerebellum and part of medulla oblongata.
• The cerebral hemispheres are oval and are separated by the great longitudinal fissure. The falx cerebri dips in this fissure. The surfaces of the hemispheres are marked by a number of winding ridges-the cerebral gyri or convolutions separated by sulci. The upturned projections are seen at the anterior extremity in front of the frontal pole called the olfactory bulbs. The occipital pole covers the mid-brain and overlies on each side, the anterior part of the cerebellum from which it is separated by the great transverse fissure which contains the tentorium cerebelli. (View image)
• The cerebellum is much smaller and conceals greater part of the medulla. Its surface shows a number of minute gyri and sulci.
• The ventral surface or the base of the brain presents the following features from behind forward
  • The median brain stem is continuous with the spinal cord behind and it consists of three parts,
    • Medulla oblongata- the posterior part which extends forward as the direct continuation of the spinal cord.
    • The pons- a transversely elongated mass which appears infront of the medulla oblongata.
    • The cerebral peduncles or crura cerebri which extend from under the pons forward and diverge to enclose the interpenduncular fossa.
  • The interpeduncular fossa is largely covered by the pituitary gland and connected to the base of the brain by a hollow tube of gray mater the infundibulum which in turn is attached to a gray body the tuber cinerium. Behind this is a white body called the mamillary body or corpus albicans. The posterior part of this space is perforated for the passage of fine blood vessels to the thalamus.
  • A band of white mater the optic tract crosses the anterior end of each cerebral peduncle and unites with its fellow and crosses to form the optic commissure or optic chiasma. This forms the anterior boundary of the interpenduncular fossa. Above and in front of the chiasma is the great longitudinal fissure.