Comparative account of Brain

All the vertebrates from fishes to mammals has well developed brain & is built based on same basic plan. However, form of brain differs in different vertebrates according to habit & behaviour of the animals.

⚫Brain of fishes,e.g.-Scoliodon

(1) Brain of Scoliodon enclosed within a cartilaginous cranium. Brain is simple, elongated, flatten & made up of three basic parts:- Forebrain, Midbrain & Hindbrain.

(2) Brain is protected by a single membrane called meninx primitiva.

(3) Olfactory lobes are large, bibbed, highly developed.

(4) Cerebral hemisphere are large, somewhat rectangular. It has no median groove.

(5) Diencephalon is small, narrow & dorsally covered with anterior extension of cerebellum.

(6) Infundibulum is ventral hollow projection behind optic chiasma.

(7) Dorsal side of the midbrain consists of two large hollow optic lobes or corpora bigemina, which remain concealed by cerebellum & control vision. Crura cerebri is poorly developed.

(8) Hind brain consist of cerebellun & medulla oblongata. cerebellum is large, elongated.

(9) Medulla oblongata is large, hollow & triangular gradually of irregular thin walled hollow outgrowths the restiform bodies.

Fig. Brain of Scoliodon A) Dorsal view B) Ventral view

C) Horizontal longitudinal section

⚫Brain of amphibians. e.g.-Frog

(1) The brain of frog is elongated somewhat flattened structure enclosed within a Bony cranium.

(2) Brain is surrounded by two membranes called meninges, & piamatter is delicate pigment & vascular & outer dura-matter is tough & fibrous.

(3) Brain consist of 3 basic parts of forebrain, midbrain & hind brain. Forebrain includes of factory lobes, two cerebral hemispheres & a diencephalon.

(4) Olfactory lobes are two, small, spherical but each contains a separate cavity called olfactory ventricle or rhinocoel.

(5) The roof of cerebrum is called pallium & each ventro-lateral side is thick called corps striatum.

(6) Diencephalon is a short, depressed region just behind the cerebrum. It has a thick lateral wall called optic thalami & thick floor called hypothalamus

(7) Midbrain bears dorso-ventrally to large rounded optic lobes corpora bigemina. Two thick, longitudinal bands of nerve fibers called crura cerebri.

(8) Hind brain includes cerebellum & medulla oblongata. cerebellum is poorly developed, small, narrow, transverse band just behind optic lobes.

(9) Medulla oblongata is the last small, conical part which is continuous with spinal cord. Its dorsal roof is thin & highly vascular forms the posterior choroid plexus.

Fig. Brain of Frog A)Dorsal view B)Ventral view

C)Horizontal longitudinal section

⚫Brain in Reptiles. e.g.-Calotes

(1) The brain is simple & similar to that of frog but comparatively it is more advanced in the relatively greater size of the cerebral hemisphere & smaller size of the olfactory lobes.

(2) Brain is divisible into three parts forebrain, midbrain & hindbrain. Forebrain consist of olfactory bulbs, cerebral hemispheres & diencephalon.

(3) Cerebral hemispheres, are a pair of oval bodies, Narrow in front & broad behind. They are clearly demarcated by a mid-dorsal groove, the median longitudinal fissure.

(4) The pallium shows an increase in thickness & number of neurons as compared with that of amphibian.

(5) Thick lateral wall of it forms optic thalami & the thick floor is called hypothalamus.

(6) Midbrain includes two large rounded optic lobes placed dorso-laterally.

(7) Hind brain includes cerebellum & medulla oblongata. cerebellum is poorly developed, narrow, flat, semicircular ridge, covering the anterior dorsal surface of a medulla. Medulla oblongata is broad in front but narrow & tapering behind.

(8) Posteriorly it shows a strong ventral plexus where it passes into the spinal cord.

Fig. Brain of Calotes A)Dorsal view B)Ventral view

C)Saggital section

⚫Brain of mammals. e.g.-Rabbit

(1) The brain of rat is protected by three membranes pia-matter, archnoid & dura-matter & built on the same plan of other vertebrate.

(2) The fore brain includes two olfactory lobes, two cerebral hemispheres & a diencephalon.

(3) Olfactory lobes attached distally to anterior end of cerebrum.

(4) Cerebral hemispheres are large pyriform, greatly developed, separated by deep sagittal fissure, overlap the Olfactory lobes in front & midbrain from behind.

(5) Diencephalon is completely covered dorsally, below backward extension of cerebral hemisphere.

(6) Midbrain consists of optic lobes which are divided forming 4 small, almost solid spherical bodies called corpora quadra gemina.

(7) Hind brain includes cerebellum & medulla oblongata.

(8) Cerebellum is divided into 5 lobes, a median vermis, two lateral loads, each terminating into a flocculus. It surface is much folded.

(9) Medulla oblongata is broad, triangular, hollow tapering & covered partly by cerebellum Restiform bodies are absent.

Fig. Brain of Rabbit A)Dorsal view B)Ventral view

C)Horizontal longitudinal section

Comparative account of Brain