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

DURAMATER

• This is a dense, tough membrane of white fibrous tissue. It has cranial and spinal parts which enclose the brain and spinal cord, respectively and continuous with each other at the foramen magnum.
• The cranial duramater is not only acting as covering of the brain but also lines the inner surface of the cranium. It is composed of two layers, an outer periosteal layer which is adherent to the internal face of the cranial bones forming the internal periosteum and an inner meningeal layer which is in contact with the arachnoid. It forms the sheath around the nerves and leaving the cranium. These two layers are mostly adherent to each other except at places where they are separated to form the venous sinuses lined by endothelium. The internal surface of the dura is also lined by endothelium and is smooth. It forms the outer boundary of the subdural space that contains a small quantity of fluid resembling lymph.
• The duramater detaches a number of infoldings between the different sections of brain and form the falx cerebri, tentorium cerebelli and a thickening diaphragm sellae or pituitary fold.
• The falx cerebri is a sickle-shaped, vertical fold of duramater situated in the midline between the two cerebral hemispheres. It is attached above to the interparietal and interfrontal crests, behind to the internal occipital protruberance and in front to the crista galli of ethmoid. Its dorsal border is convex and here the two layers of the dura are separate and enclose the dorsal longitudinal sinus. Its ventral border is concave and lies above the corpus callosum. Here again the two layers enclose the ventral longitudinal sinus. Posteriorly it joins the tentorium cerebelli.
• The tentorium cerebelli is a crescentric, transverse fold between the cerebral hemispheres and cerebellum. It is attached above to the internal occipital protuberance and laterally to the petrosal crests. Its ventral border is concave, thin and free and forms an arch over the mid brain.
• The diaphragm sellae is a thick fold of duramater on the ventral aspect of the brain, which surrounds the pituitary gland and encloses the cavernous and intercavernous sinuses. It is perforated at the middle for the infundibulum and laterally for the exit of the emergent artery of the rete mirabile cerebri and the third cranial nerve on either side of the emergent artery.
• The hypophysis cerebri or pitutary gland is an oval reddish grey coloured body about the size of a large pea situated in the sella turicia of sphenoid bone, connected at the base of the brain with a stalk and enclosed by duramater. It consists of two lobes – anterior lobe and posterior lobe. The portion which are developed from the Rathke’s pouch are included under the term adenohypophysis. These are
  • pars distalis or pars anterior,
  • pars tuberalis and
  • pars intermedia. These parts constitute the major and important portion of the gland. In other domestic animals and birds no much appreciable difference is observed other than size.
• The spinal duramater starts from the foramen magnum and terminates at the middle of the sacrum. It is composed only of the meningeal layer and forms a very loose tube around the spinal cord. It is separated from the periosteum of the spinal canal by a considerable space called epidural space and is occupied by connective tissue and fat. The dura furnishes sheaths for cranial and spinal nerves.
• The subdural space is the potential space between the dura and arachnoid with small amount of fluid, which moistens the opposed endothelial surfaces.