The grey market (or gray market) refers to the flow of goods through distribution channels other than those authorized or intended by the manufacturer or producer.

Unlike those on the black market, grey market goods are not illegal. Instead, they are being sold outside of normal distribution channels by companies which may have no relationship with the producer of the goods. Frequently this occurs when the price of an item is significantly higher in one country than another; this situation commonly occurs with cigarettes and electronic equipment such as cameras. Entrepreneurs will buy the product where it is available cheaply, often at retail but sometimes at wholesale, import it legally to the target market and sell it at a price which provides a profit, but which is below the normal market price there. Because of the nature of grey market economics, it is generally difficult or even impossible to track and verify the precise numbers of grey market sales.

Importing certain legally restricted items such as prescription drugs or firearms would be categorized as black market, as would smuggling the goods into the target country to avoid import duties.

Warranties and Grey Market Goods

Typically the manufacturer will refuse to honor the warranty of an item purchased from grey market sources, on the grounds that the higher price on the non-grey market reflects a higher level of service. This is particularly evident in electronics goods. Manufacturers may give the same model different model numbers in different countries even though the functions of the particular machine are identical. When a manufacturer identifies a particular product as not destined for that particular country the purchaser can then only seek warranty service from the manufacturer’s subsidiary in the intended country of import, not the diverted third country where the grey goods are ultimately sold by the distributor or retailer. As there is no privity of contract between the manufacturer and consumer neither the implied warranty of fitness nor the implied warranty of merchantability apply to grey market goods.

Of course, if the manufacturer sells to retailers, there’s no privity of contract between the manufacturer and the purchasor either, but the warranty applies nonetheless. Warranty law is not crystal clear, and is highly dependent on the local law.

Other Responses to the Grey Market

The parties most concerned with the grey market of a good are usually the authorized agents or importers, or the retailers, of the good in the target market. Often this is the national subsidiary of the manufacturer, or a related company, which is the local licensee of the manufacturer’s trademarks; rigorous prosecution of trademark laws to restrict advertisements for the product is thus a common tactic used to discourage the grey market, along with refusal to honour warranties and refusal to deal with distributors and retailers (and with commercial products, customers) that trade in grey market goods. Local laws (or customer demand) concerning distribution and packaging (for example, the language on labels, units of measurement, and nutritional disclosure of foodstuffs) can be brought into play, as can national standards certifications for certain goods.

Paraplegia is a condition in which the lower part of a patient’s body is paralyzed and cannot move. It is usually the result of spinal cord injury or a congenital condition such as spina bifida, but polyneuropathy may also result in paraplegia. If the arms are also paralyzed, quadriplegia is a more appropriate diagnosis.

Causes of Paraplegia

Central nervous system: Any disease process affecting the pyramidal tract of the spinal cord from the thoracic spine downward may lead to paraplegia, as this structure transmits “instructions” for movement from the brain to the anterior horn. This is the most common cause of paraplegia. It is usually spastic: it results in an increased muscle tone in the affected limbs. Causes range from trauma (acute spinal cord injury: transsection or compression of the cord, usually by bone fragments from vertebral fractures) to tumors (chronic compression of the cord), myelitis transversa and multiple sclerosis. Sometimes, paralysis of both legs can result from injury to the brain (bilateral injury of the motor cortex controlling the legs, e.g. due to a stroke or a brain tumor).

Peripheral nervous system: Rarer is the type which is caused by damage to the nerves supplying the legs. This form of damage is not usually symmetrical and would not cause paraplegia, but polyneuropathy may cause paraplegia if motor fibres are affected. While in theory the arms should also be affected, the fibres that supply the legs are longer and hence more vulnerable to damage.

Paraplegia Disability

While some people with paraplegia can walk to a degree, many are dependent on wheelchairs or other supportive measures. Impotence and various degrees of urinary and fecal incontinence are very common in those affected. Many will use catheters or adult diapers to fix these problems.

Paraplegia Complications

Due to the decreased movement and inability to walk, paraplegia may cause numerous medical complications, many of which can be prevented with good nursing care. These include pressure sores (decubitus), thrombosis and pneumonia. Physiotherapy and various assistive technology, such as a standing frame, may aid in preventing these complications.

Body-on-frame is an automobile construction technology. Mounting a separate body to a rigid frame which supports the drivetrain was the original method of building automobiles, and its use continues to this day. The original frames were made of wood (commonly ash), but steel ladder frames became common in the 1930s.

In the USA the frequent changes in automobile design made it necessary to use a ladder frame rather than monocoque to make it possible to change the design without having to change the chassis, allowing frequent changes and improvements to the car’s bodywork and interior (where they were most noticable to customers) while leaving the chassis and driveline unchanged, and thus keeping cost down and design time short. It was also easy to use the same chassis and driveline for several very different cars. Especially in the days before computer-aided design, this was a big advantage.

Most small passenger vehicles switched to unibody construction in the 1960s, leaving just trucks, buses and large cars using conventional frames. The switch continued for several decades – even SUVs typically use unibody construction today. Body-on-frame remains the preferred construction method for heavy-duty vehicles, especially those which are intended to carry and pull heavy loads.

The Lincoln Town Car dominates the American limousine market because it is the last American luxury car made with body-on-frame, which makes it easy to “stretch.”

Seat Belt

A seat belt, sometimes called a safety belt, is a harness designed to hold the occupant of a car or other vehicle in place if a collision occurs or, more commonly, if it stops suddenly. Seat belts are intended to reduce injuries by stopping the wearer from hitting hard interior elements of the vehicle or from being thrown from the vehicle. In cars, seat belts also prevent rear-seat passengers from crashing into those in the front seats.

Types of Seat Belts

Lap: Adjustable strap that goes over the waist. Used frequently in older cars, now uncommon except in some rear middle seats (also in passenger aircraft).

Two-point: A restraint system with two attachment points. A lap belt.

Automatic: Any seatbelt that closes itself automatically. Used mainly in older luxury models.

Sash: Adjustable strap that goes over the shoulder. Used mainly in the 1960s, but of limited benefit because it is very easy to slip out of in a collision.

Lap and Sash: Combination of the lap belt and the sash (two belts above). Mainly used in the 1970s, usually in the rear. Generally superseded by three-point design.

Three-point Seat Belt

Three-point: Similar to the lap and sash, but one single continuous length of webbing. Both three-point and lap-and-sash belts help spread out the energy of the moving body in a collision over the chest, pelvis, and shoulders. Until the 1980s three-point belts were commonly available only in the front seats of cars, the back seats having only lap belts. Evidence of the potential for lap belts to cause separation of the lumbar vertebrae and the sometimes associated paralysis, or “seat belt syndrome”, has led to a revision of safety regulations in nearly all of the developed world requiring that all seats in a vehicle be equipped with three-point belts. By September 1, 2007, all new cars sold in the U.S. will require a lap and shoulder belt in the center rear.

Five-point harness: A safer but more restrictive seat belt. Five-point harnesses are typically found in child safety seats and in racing cars. The lap portion is connected to a belt between the legs and there are two shoulder belts, making a total of five points of attachment to the seat.

Six-point harness: This belt is like a five-point harness but includes an extra belt between the legs. Six-point harnesses are used mainly in racing. In NASCAR, the six-point harness became popular after the death of Dale Earnhardt. Earnhardt was wearing a five-point harness when he crashed and died. Because it was thought at first that his belt had broken, some teams ordered a six-point harness. The sixth point has two belts between the legs, which is seen by some to be a weaker point than the other parts.

Inertia reel: Used almost universally today, inertia reel belts are effectively self-adjusting, which improves effectiveness. They also retract when not in use, reducing the chances of damage to the belts. A retractor reel lets out the strap or pulls it back as needed, and in the event of an accident the reel locks, preventing any more strap to come out and holding the passenger in the car. This may be augmented by pretensioners. Most three-point belts are of inertia-reel construction, and some lap-and-sash and lap belts.

Seat Belt History

Seat belts were first invented by George Cayley in the 1800s. Seat belts were introduced in aircraft for the first time in 1913 and became common in the 1930s. The automotive seat belt was introduced into the United States by Kenneth Ligon and his brother, Bob Ligon, whose patented quick release seat belt, the AutoCrat Safety Belt, was the first seat belt installed as original equipment in the U.S. by Ford in its 1956 model year. The first seatbelt to be included as standard was on the 1959 Volvo. Australia was the first country to make seatbelts compulsory in vehicles. However, they were not required by law in the U.S. on passenger vehicles until the 1968 model year.

Three point harnesses were first made readily available in mass-produced vehicles by Volvo. It was Swedish engineer Nils Bohlin who patented the modern three-point belt design and gave it to Volvo.

Seat Belt Mechanism

Most seat belts are equipped with locking mechanisms that tighten the belt when pulled hard (e.g. by the force of a passenger’s body during a crash) but do not tighten when pulled slowly. Many are also equipped with ‘pretensioners’, which preemptively tighten the belt to prevent the passenger from jerking forward in a crash.

Mercedes-Benz first introduced pretensioners on the 1981 S-Class. In the event of a crash, a pretensioner will tighten the belt almost instantaneously. This reduces the load on the occupant in a violent crash. Like airbags, pretensioners are triggered by sensors in the car’s body, and most pretensioners use explosively expanding gas to drive a piston that retracts the belt. Pretensioners also lower the risk of “submarining”, which is when a passenger slides forward under a loosely worn seat belt.

Seat Belt Legislation and Risk Compensation

The issue of seat belt legislation has been a source of some controversy. Hospital based studies of car accident victims, experiments using both crash test dummies and actual human cadavers have indicated that wearing seat belts should provide a reduced risk of death and injury in many types of car crashes. This has led many countries to adopt mandatory seat belt wearing laws. It is generally accepted that, in comparing like-for-like accidents, a vehicle occupant wearing a properly fitted seatbelt has a significantly lower chance of death or serious injury. Within the USA, 49 states now require adults to wear seat-belts; New Hampshire has no such law.

The effects of such laws are disputed, stemming from the observed fact that no country is able to demonstrate a reduction in road fatalities due to passage of a seat belt law, though deaths have in some cases been migrated from drivers to other road users. This has influenced the development of the risk compensation theory, which says that drivers adjust their behaviour in response to the increased sense of personal safety wearing a seat belt provides. In one trial, habitual wearers and non-wearers were asked to drive around a course a number of times under the pretence of testing different seat belt materials for comfort. It was found that non-wearers drove consistently faster when belted than when unbelted (similar responses have been shown in respect of ABS braking and, more recently, airbags). It is also possible that the types of injury modelled in the trials were only a subset of potential serious injuries – for example, oblique impacts may produce twisting forces on the head leading to diffuse axonal injury, a particularly serious type of brain injury.

Put simply, if one is involved in a crash, one is almost always better off wearing a seat belt. However, the probability of being in a crash in the first place may be affected by the fact that the person feels safer, so the overall safety benefit may be offset to some unspecified degree.

Quadriplegia, also known as tetraplegia, is a symptom in which a human experiences partial or complete paralysis from the neck down.

It is caused by damage to the brain or to the spinal cord at a high level (e.g. spinal cord injuries secondary to an injury to the cervical spine). The injury causes the victim to lose total or partial use of the arms and legs. The condition is also termed tetraplegia; both terms mean “paralysis of four limbs”, however tetraplegia is becoming the more accepted term for this condition. Tetraplegia, used commonly in Europe, is the more etymologically correct version since both “tetra” and “plegia” are Greek roots whereas “quadra” is a Latin root.

There are about 5000 cervical spinal cord injuries per year in the United States and about 1000 per year in the UK. In 1988, it was estimated that lifetime care of a 27-year-old rendered tetraparetic was about US $1 million and that the total national costs were US $5.6 billion per year.

Delayed diagnosis of cervical spine injury has grave consequences for the victim. About one in twenty cervical fractures are missed, and about two-thirds of these patients suffer further spinal cord damage as a result. About 30% of cases of delayed diagnosis of cervical spine injury develop permanent neurological deficits.

In some rare cases, through intensive rehabilitation, slight movement can be regained through “rewiring” neural connections as in the case of late actor Christopher Reeve.

Spinal cord injury, or myelopathy, is a disturbance of the spinal cord that results in loss of sensation and mobility. The two common types of spinal cord injury are:

Trauma: automobile accidents, falls, gunshots, diving accidents, etc.

Disease: polio, spina bifida, tumors, Friedreich’s ataxia, etc.

It is important to note that the spinal cord does not have to be completely severed for there to be a loss of function. In fact, the spinal cord remains intact in most cases of spinal cord injury.

Spinal cord injuries are not the same as back injuries such as ruptured disks, spinal stenosis or pinched nerves. It is possible to “break one’s neck or back” and not sustain a spinal cord injury if only the vertebrae are damaged, but the spinal cord remains intact.

About 450,000 people in the United States live with spinal cord injury, and there are about 11,000 new spinal cord injuries every year. The majority of them (78%) involve males between the ages of 16-30 and result from motor vehicle accidents (42%), violence (24%), or falls (22%).

The Insurance Institute for Highway Safety is a U.S. non-profit organization funded by auto insurers. It works to reduce the number of motor vehicle crashes, and the rate of injuries and amount of property damage in the crashes that still occur. It carries out basic research and produces ratings for each model of vehicle.

The Institute’s crash testing differs from NHTSA’s New Car Assessment Program (governmental) in that the Insurance Institute for Highway Safety tests are ‘offset’ from the center. These ‘offset’ tests expose 40% of the front of the vehicle to an impact with a deformable barrier at approximately 40 mph. Because only 40% of the vehicle’s front must stand the impact, it shows the structural strength much better than the U.S. Government’s NHTSA New Car Assessment Program full-width testing. Many real-life frontal impacts are offset.

The IIHS uses four ratings for each category, Good (best, green G), Acceptable (yellow A), Marginal (orange M) and Poor (worst, red P). Vehicles which score Good in all the various rating categories, or which have only one Acceptable category, are given Best Pick designations.

As with NHTSA’s New Car Assessment Program testings, vehicles across different categories may not be directly compared, as increased weight is beneficial in a two-vehicle crash.

Relatively new to the IIHS is the side impact test. Unlike NHTSA New Car Assessment Program test’s low barrier, the IIHS uses an elevated barrier to simulate the impact of an sport utility vehicle (approximately half of all new cars sold) into the side of the vehicle being tested. This is a “very demanding” test of both the structural integrity of the vehicle, as well as the restraints. While most new vehicles achieve 4 and 5 stars from the NHTSA (where head injuries are not part of the rating), many do not score well in the IIHS side impact test. Side impact airbags greatly help vehicles score higher in the test. The IIHS side impact test more accurately reflects a real side impact involving an SUV as the vehicle that impacts into the side of another.

The IIHS also evaluates vehicles’ bumpers in a series of 5-mph impacts, as well as seat and head restraint designs in relation to rear-impact protection, using the same Poor-Good rating system.

When purchasing a new vehicle, it is necessary to pay attention to both the IIHS and NHTSA test. For example, a Chevrolet Venture (also marketed as Oldsmobile Silhouette, Pontiac Montana/TransSport) achieves a respectable rating of 4/5 stars from NHTSA, but is rated Poor by the IIHS for its poor structural integrity which becomes apparent in the offset crash test.

NHTSA test of the Chevy Venture.

Insurance Institute for Highway Safety test of Chevy Venture (1997 Pontiac Trans Sport tested).

Insurance Institute for Highway Safety test of Chevy Venture (post-crash, 1997 Pontiac Trans Sport tested).

The difference of results between the same model tested by the NHTSA and IIHS are great and must be considered when deciding the safety of a vehicle.

2004 Toyota Prius - a hybrid gas-electric vehicle.

A hybrid vehicle is a vehicle using an on-board Rechargeable energy storage system (RESS) and a fueled propulsion power source for vehicle propulsion. They are low-polluting and low-petro consuming cars. The different propulsion power systems may have common subsystems or components.

The term most commonly refers to petroleum-electric hybrid vehicles, also called Hybrid-electric vehicle (HEV) which use gasoline (petrol) or diesel to power internal-combustion engines (ICEs), and electric batteries to power electric motors. Modern mass-produced hybrids, such as the Toyota Prius, recharge their batteries by capturing kinetic energy via regenerative braking. As well, when cruising or in other situations where just light thrust is needed, “full” hybrids such as the Prius can use the combustion engine to generate electricity by spinning a generator (often a second electric motor) to either recharge the battery or directly feed power to an electric motor that drives the vehicle. This contrasts with all-electric cars which use batteries charged by an external source such as the grid, or a range extending trailer. Nearly all hybrids still require gasoline and diesel as their sole fuel source though other fuels such as ethanol or plant based oils have also seen occasional use. Hybrid cars also use Hydrogen gas.

The term hybrid when used in relation with cars also has other uses. Prior to its modern meaning of hybrid propulsion, the word hybrid was used in the United States to mean a vehicle of mixed national origin; generally, a European car fitted with American mechanical components. This meaning has fallen out of use. In the import scene, hybrid was often used to describe an engine swap, such as the common Honda B16 engine into a Honda Civic. Some have also referred to flexible-fuel vehicles as hybrids because they can use a mixture of different fuels — typically gasoline and ethanol alcohol fuel. There are not diesel flexible-fuel vehicles, because nowadays diesel cars can use petroleum and biodiesel at the same time.

Hybrid Vehicle History

In 1898 Ferdinand Porsche designed the Lohner-Porsche carriage, a series-hybrid vehicle that used a one-cylinder gasoline internal combustion engine that spun a generator which powered four wheel-mounted electric motors. The car was presented at the 1900 World Exhibition in Paris. The up to 56 km/h (35 mph) fast carriage broke several Austrian speed records, and also won the Exelberg Rally in 1901 with Porsche himself driving. Over 300 of the Lohner-Porsche carriages were sold to the public.

In 1959 the development of the first transistor-based electric car – the Henney Kilowatt – heralded the development of the electronic speed control that paved the way for modern hybrid electric cars. The Henney Kilowatt was the first modern production electric vehicle and was developed by a cooperative effort between National Union Electric Company, Henney Coachworks, Renault, and the Eureka Williams Company. Although sales of the Kilowatt were dismal, the development of the Kilowatt served was a historical “who’s who” of electric propulsion technology.

A more recent working prototype of the electric-hybrid vehicle was built by Victor Wouk (one of the scientists involved with the Henney Kilowatt and also brother of author Herman Wouk ). Wouk’s work with electric hybrid vehicles in the 1960s and 1970s earned him the title “Godfather of the Hybrid”. Wouk installed a prototype electric-hybrid drivetrain into a 1972 Buick Skylark provided by GM for the 1970 Federal Clean Car Incentive Program, but the program was killed by the EPA in 1976. Since then, hobbyists have continued to build hybrids but none were put into mass production by a major manufacturer until the waning years of the twentieth century.

The regenerative-braking hybrid, the core design concept of most production hybrids, was developed by Electrical Engineer David Arthurs around 1978 using off-the shelf components and an Opel GT. However, the voltage controller to link the batteries, motor (a jet-engine starter motor), and DC generator was Mr. Arthurs’. The vehicle exhibited ~75 mpg fuel efficiency and plans for it (as well as somewhat updated versions) are still available through the Mother Earth News website. The Mother Earth News’ own 1980 version of the regenerative-braking hybrid claimed nearly 84 mpg.

The Bill Clinton administration initiated the Partnership for a New Generation of Vehicles (PNGV) program in September 29, 1993 that involved Chrysler, Ford, General Motors, USCAR, the DoE, and other various governmental agencies to engineer the next efficient and clean vehicle. The NRC cited automakers’ moves to produce hybrid electric vehicles as evidence that technologies developed under PNGV were being rapidly adopted on production lines, as called for under Goal 2. Based on information received from automakers, NRC reviewers questioned whether the “Big Three” would be able to move from the concept phase to cost effective, pre-production prototype vehicles by 2004, as set out in Goal 3. [Review of the Research Program of the Partnership for a New Generation of Vehicles: Seventh Report, National Research Council, (2001), p. 77].

The program was replaced by the hydrogen focused FreedomCAR initiative of George W. Bush’s administration in 2001. The focus of the FreedomCAR initiative being to fund research too high risk for the private sector to engage in with the long term goal of developing emission / petroleum free vehicles.

In the intervening period, the widest use of hybrid technology was actually in diesel-electric submarines, which operate in essentially the same manner as hybrid electric cars. However, in this case the goal was to allow operation underwater without consuming large amounts of oxygen, rather than economizing on fuel. Since then, many submarines have moved to nuclear power, which can operate underwater indefinitely, though a number of nations continue to rely on diesel-electric fleets.

Automotive hybrid technology became successful in the 1990s when the Honda Insight and Toyota Prius became available. These vehicles have a direct linkage from the internal combustion engine to the driven wheels, so the engine can provide acceleration power. The 2000s saw development of plug-in hybrid electric vehicles (PHEVs), which can be recharged from the electrical power grid and do not require conventional fuel for short trips. The Renault Kangoo was the first production model of this design, released in France in 2003. However, the environmental benefits of plug-in hybrids depend somewhat on the source of the electrical power. In particular, electricity generated with wind would be cleaner than electricity generated with coal, the most polluting source. On the other hand, electricity generated with coal in a central power plant is still much cleaner than pure gasoline propulsion, due to the much greater efficiencies of a central plant. Furthermore, coal is only one source of centrally generated power, and in some places such as California is only a minor contributor, overshadowed by natural gas and other cleaner sources.

The Prius has been in high demand since its introduction. Newer designs have more conventional appearance and are less expensive, often appearing and performing identically to their non-hybrid counterparts while delivering 50% better fuel efficiency. The Honda Civic Hybrid appears identical to the non-hybrid version, for instance, but delivers about 50 US mpg (4.7 L/100km). The redesigned 2004 Toyota Prius improved passenger room, cargo area, and power output, while increasing energy efficiency and reducing emissions. The Honda Insight, while not matching the demand of the Prius, is still being produced and has a devoted base of owners. Honda has also released a hybrid version of the Accord.

2005 saw the first hybrid SUV released, Ford Motor Company’s Ford Escape Hybrid. Toyota and Ford entered into a licensing agreement in March 2004 allowing Ford to use 20 patents from Toyota related to hybrid technology, although Ford’s engine was independently designed and built. In exchange for the hybrid licences, Ford licensed patents involving their European diesel engines to Toyota. Toyota announced model year 2005 hybrid versions of the Toyota Highlander and Lexus RX 400h with 4WD-i which uses a rear electric motor to power the rear wheels negating the need for a differential. Toyota also plans to add hybrid drivetrains to every model it sells in the coming decade.

For 2007 Lexus is offering a hybrid version of their GS sport sedan dubbed the GS450h with “well in excess of 300hp”. The 2007 Camry Hybrid has been announced and is slated to launch in late Spring as a 2007 model. It will be built in Kentucky, USA. Also, Nissan announced the release of the Altima hybrid (technology supplied by Toyota) around 2007.

An R.L. Polk survey of 2003 model year cars showed that hybrid car registrations in the United States rose to 43,435 cars, a 25.8 % increase from 2002 numbers. California, the nation’s most populous state at one-eighth of the total population, had the most hybrid cars registered: 11,425. The proportionally high number may be partially due to the state’s higher gasoline prices and stricter emissions rules, which hybrids generally have little trouble passing.

Honda, which offers Insight, Civic and Accord hybrids, sol 26,773 hybrids in the first 11 months of 2004. Toyota has sold a cumulative 306,862 hybrids between 1997 and November 2004, and Honda has sold a total of 81,867 hybrids between 1999 and November 2004.

A chassis (plural: “chassis”) consists of a framework which supports an inanimate object.

In the case of a motor vehicle, the term chassis means the frame plus the “running gear” like engine, transmission, driveshaft, differential, and suspension. A body (sometimes referred to as “coachwork”), which is usually not necessary for integrity of the structure, is built on the chassis to complete the vehicle.

In an airplane the chassis consists only of the landing gear or undercarriage, not the airframe itself.

Central Nervous System

The central nervous system (CNS) represents the largest part of the nervous system. Together with the peripheral nervous system, it has a fundamental role in the control of behavior.

Since the strong theoretical influence of cybernetics in the fifties, the CNS is conceived as a system devoted to information processing, where an appropriate motor output is computed as a response to a sensory input. Yet, many threads of research suggest that motor activity exists well before the maturation of the sensory systems and then, that the senses only influence behavior without dictating it. This has brought the conception of the CNS as an autonomous system.

The CNS originates from the neural plate, a specialised region of the ectoderm, the most external of the three embryonic layers. During embryonic development, the neural plate folds and forms the neural tube. The internal cavity of the neural tube will give rise to the ventricular system. The regions of the neural tube will differentiate progressively into transversal systems. First, the whole neural tube will differentiate into its two major subdivisions: spinal cord (caudal) and brain (rostral). Consecutively, the brain will differentiate into brainstem and prosencephalon. Later, the brainstem will subdivide into rhombencephalon and mesencephalon, and the prosencephalon into diencephalon and telencephalon.

The CNS is covered by the meninges, the brain is protected by the skull and the spinal cord by the vertebrae. The rhombencephalon gives rise to the pons, the cerebellum and the medulla oblongata, its cavity becomes the fourth ventricle. The mesencephalon gives rise to the tectum, pretectum, cerebral peduncle and its cavity develops into the mesencephalic duct or cerebral aqueduct. The diencephalon gives rise to the subthalamus, hypothalamus, thalamus and epithalamus, its cavity to the third ventricle. Finally, the telencephalon gives rise to the striatum (caudate nucleus and putamen), the hippocampus and the neocortex, its cavity becomes the lateral (first and second) ventricles.

The basic pattern of the CNS is highly conserved throughout the different species of vertebrates and during evolution. The major trend that can be observed is towards a progressive telencephalisation: while in the reptilian brain that region is only an appendix to the large olfactory bulb, it represent most of the volume of the mammalian CNS. In the human brain, the telencephalon covers most of the diencephalon and the mesencephalon. Indeed, the allometric study of brain size among different species shows a striking continuity from rats to whales, and allows us to complete the knowledge about the evolution of the CNS obtained through cranial endocasts.