Question

. Describe how the brain has evolved across this spectrum of animals. (Shark, Mudpuppy,snake, bird, and pig)

Answer 1

COMPARATIVE ACCOUNT OF BRAIN

		FISH	AMPHIBIA	REPTILIA	AVES	MAMMALIA
	Characters	Shark	Mudpuppy	Snake	Bird	Pig
	Cranium	Cartilaginous	Bony	Bony	Bony	Bony
	Size	Simple, Elongated, Flattened, thrice as long as broad	Simple, elongated, flattened nearly 3 times longer than broad	Elongated but comparatively larger and broader	Brain relatively larger and more complex	Brain relatively largest, complex and most advanced.
	Main Parts- Forebrain, Midbrain and Hindbrain	Present	Present	Present	Present	Present

FOREBRAIN

1. OLFACTORY LOBES

Position	attached to antero- lateral angles of cerebrum	attached side by side in front of cerebrum	attached in front of cerebrum without constrictions	attached anteriorly to cerebral hemispheres	attached distinctly to anterior end of cerebrum
Parts	Differentiated into tract and bulb	No differentiation between tract and bulb	Each drawn into an olfactory bulb	No distinctions into penducles and bulbs	Tracts covered beneath cerebrum.
Olfactory ventricles- Rhinocoels	Spacious	Small and narrow	Narrow	Absent	Present

2. CEREBRAL HEMISPHERES

Neuropore	Present	Absent	Absent	Absent	Absent
Cerebral cortex	Absent	Shows beginning of cerebral cortex	Poorly developed	Relatively poor than in mammals	Very well developed
Pallium	Poorly developed	Developed better than in fishes	Shows an increase	Relatively poor than in mammals	Very well developed
Corpora striata	Poorly developed	Developed better than in fishes	Thick, well developed	Thick, very conspicuous	Comparatively, less developed
Corpus callosum	Absent	Absent	Absent	Absent	Present
Lateral ventricles- Paracoels	Spacious and unbranched	Unbranched	Unbranched	Unbranched	Well developed and branched

3. DIENCEPHALON

Shape and Size	Small, narrow and dorsally coverd beneath anterior extension of cerebellum	Short, rhomboidal and not covered dorsally by cerebellum	Small, rounded and covered dorsally by cerebral hemispheres and optic lobes	Dorsal surface covered by cerebrum and cerebellum	Completely covered dorsally below backward extension of cerebral hemispheres
Corpus albicans	Absent	Absent	Absent	Absent	Present
Middle commissure	Absent	Absent	Absent	Absent	Present

MIDBRAIN

Optic lobes	Dorsal side contains two large optic lobes which remain mostly concealed by cerebellum	Dorsal surface has two uncoverd, lateral. rounded and hollow optic lobes.	Two medium, oval dorso-lateral lobes which remains uncovered	Two optic lobes laterally displaced	Optic lobes form four small solid bodies mostly covered by cerebral hemispheres
Crura cerebri	Poorly developed and mostly concealed ventrally by inferior lobes and saccus vasculosus	Run longitufinally beneath optic lobes connecting diencephalon and medulla. Partially covered by pituitary	Thickened floor forms crura cerebi which are comparatively less developed	Bands of ventral crura cerebi thickened	Far better developed than others

HINDBRAIN
1. CEREBELLUM

Division	Made of three lobes divided by two transverse furrows	Undivided	Remains undivided	Divided into three lobes: a large median vermis, and two small lateral flocculi	Divided into five lobes: a median vermis, two lateral lobes each terminating into a flocculus
Surface	Dorsal surface bears irregular folds	Surface is smooth without folds	External surface is smooth	Surface folded all over	Surface much folded
Ventricle	Cavity	Small Cavity	Small Cavity	Solid Cavity	Narrow and branched
Arbor vitae	Absent	Absent	Absent	Absent	White matter looks tree-like
Pons varolli	Absent	Absent	Absent	Absent	Stout, ventral transverse nervous band connecting two lateral sides of cerebellum

2. MEDULLA OBLONGATA

Shape and Size	Large, hollow, triangular gradually tapering behind, partly concealed in front under cerebellum	Small, conical hollow uncovered	Small, conical hollow uncovered	Small, hollow concealed beneath cerebellum	Broad, triangular, hollow, tapering and covered partially by cerebellum
Restiform bodies	Medulla bears antero-laterally a pair of irregular, thin-walled, hollow outgrowths.	Absent	Absent	Absent	Absent
Ventral flexure	Absent	Absent	Medulla and spinal cord meet at a ventral flexure	Well- marked	Absent

CRANIAL NERVES

Number	10 pairs	10 pairs	12 pairs. XI is spinal accessory and XII is hypoglossal	12 pairs. XI is spinal accessory and XII is hypoglossal	12 pairs. XI is spinal accessory and XII is hypoglossal