The invention relates to an exhaust gas system for internal combustion engines, in particular in vehicles with combustion engines, in particular Diesel engines. The internal combustion engine has an exhaust manifold which supplies exhaust gases to a catalytic converter which is arranged in a housing part that is spaced from the exhaust manifold. The exhaust manifold and the exhaust gas system are intended to supply the catalytic converter with a sufficient quantity of exhaust gases and to heat the catalytic converter as uniformly as possible. The invention relates in particular to a fuel-operated heating of the catalytic converter, wherein the exhaust gas system comprises a heating line which leads from an exhaust line, which leads from an exhaust gas recirculation line which leads into the exhaust manifold and leads from the exhaust manifold via an exhaust gas inlet line to a branching point in the exhaust gas inlet line at which the branching point opens into the heating line. Such an exhaust gas system for internal combustion engines is known from EP 875 722 B1. Here, the two-part exhaust manifold has a casing which is configured in the form of a cast part. The exhaust manifold, which comprises exhaust gas collecting chambers in the casing, is used to introduce the exhaust gas into the exhaust line. A heating of the catalytic converter is carried out by the two-part exhaust manifold as follows. The heating line leads from the exhaust line, by way of the exhaust gas inlet line and the branching point, which is arranged at an exhaust gas outlet side of the exhaust manifold, into the interior of the exhaust manifold. This is carried out in that an insulating housing component, which encloses an end region of the heating line and is welded at this end, is inserted into the exhaust manifold and is welded to the latter. However, due to the use of a welded connection between the insulating housing component and the exhaust manifold, high production tolerances must be taken into account. It is therefore an object of the present invention to provide an exhaust gas system which is improved with regard to production tolerances. In addition, the exhaust gas system should have a long service life. This and other objects are achieved by an exhaust gas system for internal combustion engines, particularly in vehicles, which comprises an exhaust manifold through which exhaust gases pass and which comprises at least one catalytic converter which is heated. A housing part of the exhaust manifold is closed by a cast-on closing part that carries a catalytic converter lining with a central opening and has a receiving chamber for receiving the catalytic converter. The exhaust gas system further comprises a heating line that is connected to the exhaust manifold by means of a branched pipe. The receiving chamber of the closed housing part has a receiving region for receiving the branched pipe. The receiving region is connected to the inlet region of the receiving chamber so as to form an exhaust gas channel between the receiving region and the inlet region. The invention is based on the general idea of avoiding a welded connection between an insulating housing component and an exhaust manifold and on using a cast-on closing part of the housing part to provide the connection for a heating line. The use of a housing part and the use of a cast-on closing part of the housing part provide a large degree of freedom in production which enables very low production tolerances. Such a low production tolerance is desirable particularly in the production of an exhaust manifold with catalytic converters on exhaust manifolds which are exposed to a high thermal and mechanical stress due to the exhaust gas temperature and the exhaust gas flow in the system, since these stresses have an unfavorable effect on the production tolerances and lead to premature wear in the exhaust system. Moreover, a cast-on closing part has the advantage that tolerances can be compensated more easily due to the relative movement between cast-on components and injection molded components, for example, due to a shrinkage process or due to heating and cooling. In one preferred embodiment, the housing part and the casting are configured so that the housing part and the casting are integrally joined to one another. Such a connection between the housing part and the casting is particularly advantageous since, in addition to the thermal shock resistance that can be obtained, it enables a compact design of the exhaust gas system. In another preferred embodiment, the casting and the receiving region are configured so that they can be detached from one another. In this case, the connection between the casting and the receiving region can be detached from one another and taken along when the catalytic converter is replaced. The casting can subsequently be attached to another housing part of the exhaust manifold. In another preferred embodiment, the receiving region has a receiving space which is open on a top side and has a connecting region on the top side for connecting the heating line. This arrangement of the connecting region provides, in a particularly simple manner, a simple feeding of the heating line into the receiving space. The connection between the heating line and the top side of the receiving region takes place particularly in that the end of the heating line can be inserted into the receiving space from outside. Alternatively or additionally, a connection can be provided in the receiving space by means of welding or plugging the heating line into the receiving space. In another preferred embodiment, the casting and the receiving region form a receiving space which is open on a top side, and wherein the heating line is configured so that, when the heating line is connected, it extends on the top side of the receiving region. In this case, the arrangement of the heating line in the region of the receiving region ensures that the heat can be effectively conducted to the catalytic converter. The heating can then also be improved due to the fact that the exhaust gas manifold is connected to the catalytic converter by means of the inlet side on the branching part and can therefore be heated directly at the top side. In yet another preferred embodiment, the outer contours of the receiving region and the casting are formed approximately identically. The approximately identically configured outer contours provide a compact design of the exhaust gas system. It is also possible to connect the receiving region and the casting to one another at different heights, for example, so that there is a temperature gradient in the vicinity of the catalytic converter. This improves the flow of heat in the interior of the exhaust manifold. The invention can be implemented by means of at least one exhaust gas treatment component in the exhaust gas system. The components preferably are configured to reduce the pollutant emissions in the exhaust gas of the internal combustion engine. In one preferred embodiment, a catalytic converter with a three-way catalyst or a NOx storage catalyst is used. This type of catalytic converter is also called a xe2x80x9cdeNOx component.xe2x80x9d In another preferred embodiment, a particulate filter, which contains a ceramic or metallic honeycomb body, is used. The honeycomb body is, in turn, preferably wound from sheet metal bands. The internal diameter of the honeycomb body can be set to vary within certain limits in order to satisfy different demands, for example, regarding flow resistance, strength and the like. The present invention further relates to an exhaust gas system for internal combustion engines, particularly in vehicles, comprising at least one catalytic converter which is heated by exhaust gases. An exhaust gas system comprises a heating line which leads from an exhaust line to the exhaust manifold of the internal combustion engine. An exhaust manifold has a housing part which is configured in the form of a cast part and is closed by a cast-on closing part. The cast-on closing part carries a catalytic converter lining with a central opening. A receiving region is formed on the housing part in a region between the top side of the housing part and the casing of the catalytic converter. A receiving chamber for receiving the catalytic converter is formed in the receiving region. The heat line is inserted into the receiving chamber from a top side of the receiving region. The exhaust gas system further comprises an insert component which has a through-opening. A receiving region is formed in the insert component and is configured so that the insert component can be inserted into the receiving region. The receiving region is connected