Let us learn about the comparison of brain between toad, lizard, pigeon and pig.
Comparison # Toad:
1. Forebrain:
The two olfactory lobes are fused together anteriorly. Olfactory peduncle is absent. These lobes are responsible for the sense of smell.
2. Cerebral Hemispheres:
Cerebral hemispheres are divided by a longitudinal fissure. The roof of the hemisphere is thick, smooth and nervous. Corpora striata are poorly developed and are connected by anterior commissures. Lumen of each hemisphere is reduced by the thickening of its lateral and median wall. Cerebrum is the centre for intelligence, conscience and control of voluntary muscles.
On the dorsal side of the diencephalon epiphysis is small. Pineal body of unknown function. Anterior choroid plexus is present. Ventral side of the diencephalon bears an x- shaped optic chiasma. Presence of infundibulum and pituitary body. The lateral sides of the diencephalon are thick to form optic thalami.
3. Midbrain:
Optic lobes are large and hollow ovoid bodies and two in number. Crura cerebri are longitudinally placed nerve fibres-like structures placed ventrally. Optocoels are present.
4. Hind Brain:
Cerebellum is small and does not overlap the structures in front and behind. It represents a thin transverse band-like structure.
5. Medulla Oblongata:
Medulla oblongata is thick and gradually tapers behind as a spinal cord. It gives rise 4 pairs of cranial nerves. The roof of the medulla oblongata is formed by a thin vascular membrane, called the posterior choroid plexus. The corpora restiformia are absent in medulla oblongata. It regulates the breathing, heartbeat, and metabolism.
Comparison # Lizard:
1. Forebrain:
Olfactory lobes are small and connected to the brain by olfactory peduncle.
2. Cerebral Hemispheres:
Cerebral hemispheres are larger than amphibians. The two hemispheres are elongated and are separated medially by a deep fissure. The dorsal surface of the hemispheres is smooth and thin but the lateral and ventral walls are thick that constitute the corpora striata.
Due to accumulation of large amount of grey matters the roof of cerebral hemispheres is called neopallium. On the dorsal surface of the diencephalon there are tub projections, called parietal organ, situated at the anterior of the pineal body.
Another projection, called paraphysis, which is present in reduced condition. On the ventral side hangs infundibulum and pituitary body. Lateral ventricles of the cerebral hemispheres are less spacious. Hippocampal lobes are differentiated. Anterior commissures and corpus albicans are absent.
3. Midbrain:
Optic lobes are more developed than those of amphibia and two in number, called corpora bigemina. They are hollow with optocoels. Crura cerebri at the floor and poorly developed.
4. Hind Brain:
Cerebellum is very small, semicircular and flap-like. It contains ventricle. Floccular lobes and pons varolii are absent. The surface of the cerebellum is smooth.
5. Medulla Oblongata:
Medulla oblongata tapers gradually and joins with the spinal cord. Its roof is thin and vascular that forms the posterior choroid plexus.
Comparison # Pigeon
1. Forebrain:
Olfactory lobes are reduced. Olfactory bulbs and tract are much reduced.
2. Cerebral Hemispheres:
Cerebral hemispheres exhibit considerable increase in size. These two lobes are separated by a median dorsal fissure. Corpora striata are prominent that reduces the lateral ventricles to very narrow spaces.
The corpus striatum is differentiated into hyper-striatum, meso-striatum and palaeo-striatum. The roof of cerebral hemispheres is called neopallium. The neopallium is un-convoluted. The diencephalon is inconspicuous and completely covered by cerebral hemispheres and cerebellum.
3. Midbrain:
Two large optic lobes with optocoels much reduced. Crura cerebri are well developed.
4. Hind Brain:
Cerebellum is more advanced than the reptilian cerebellum. It is divided two lateral and one median lobe. The median lobe is called vermis and lateral lobes are called flocculi. It is solid because the 4th ventricle does not extend it. Generally surface is extensively folded.
5. Medulla Oblongata:
Medulla tapers and joins with the spinal cord. Posterior choroid plexus is completely covered by cerebellum. Ventral flexure is highly developed.
Comparison # Guinea-Pig
1. Forebrain:
Olfactory lobes are small and club- shaped. Olfactory peduncle is absent.
2. Cerebral Hemispheres:
Cerebral hemispheres are very large. They occupy two-thirds of the whole brain. The two cerebral hemispheres are connected by a band of nerve tracts that connect ventrally, called corpus callosum. Each hemisphere is subdivided into 4 lobes, called frontal, parietal, temporal and occipital, by grooves, called Sylvian fissure. Neopallium is highly developed. Presence of corpus albicans.
3. Midbrain:
Optic lobes are small and four in number (corpora quadrigemina) Optocoels are highly developed.
4. Hind Brain:
Cerebellum is more complex and highly advanced than the cerebellum of pigeons. It is large, elongated and solid. It is subdivided into 5 lobes — namely a median vermis, two lateral lobes and two flocculi. The surface of cerebellum is thrown into numerous folds, called gyri and grooves between the folds called sulci.
On the ventral side the two halves of the cerebellum are connected by a broad band, known as pons varolii.
5. Medulla Oblongata:
The lateral walls and floor of the medulla are highly thickened. Its roof forms highly vascularized posterior choroid plexus.
