The kinematics of a galactic bulge are somewhat harder to determine than are the kinematics of an elliptical galaxy: light from the surrounding disk contaminates the observable properties of the bulge, and obscuration due to dust frequently further complicates the analysis. On the positive side, however, the presence of a disk with measurable inclination defines a direction which might reasonably be expected to define one of the principal axes of the bulge — a piece of information that is generally difficult to obtain in the case of elliptical galaxies.
Observations of the bulge of a disk galaxy that lies reasonably close to face-on allow us to measure its central velocity dispersion with little contamination from the disk. Combining such kinematic measurements with the bulge's gross photometric properties suggests that these systems respect the same fundamental plane as elliptical galaxies and therefore satisfy the standard 
relation of equation (A) (Dressier 1987). This similarity between the properties of bulges and ellipticals presumably reflects some common aspect of their formation and evolution, but since we do not yet have a clear understanding of the nature of the fundamental plane, the significance of this discovery is still unclear.
As we have discussed above, the contribution to the total luminosity from the disk increases as we look to larger distances from the center of the galaxy. On these larger scales it therefore becomes difficult to isolate the bulge kinematics in the PV diagram. One solution to this problem is to observe early-type disk galaxies in which the bulge is so dominant that disk contamination is small, but the large bulges which can be observed by this approach may not be representative. Alternatively, observations of the bulges of edge-on galaxies, can be used: the surface brightness of the disk drops rapidly with distance from the galaxy's plane , so we see fairly pure bulge kinematics in regions away from the major axis of an edge-on system.
Figure 1 Values of (v/
)* for a sample of spheroidal systems as a function of their absolute blue magnitudes, Mg. Elliptical galaxies are shown as circles, with unfilled circles indicating dwarf spheroidal systems. The bulges of disk galaxies are shown as circles with lines through them. In a number of cases no rotation was detected, so only upper limits are quoted for (v/)* *. [From the data published in Davies & Illingworth (1983), Davies et al. (1983) and Bender & Nieto (1990)]
Kinematic maps derived from observations of edge-on galaxies reveal that bulge kinematics vary smoothly with distance from the galaxies' central planes. Consequently, some estimate can be made of a bulge's major-axis kinematics by extrapolating off-axis observations down to the plane of the galaxy. We can thus estimate values 
galaxy bulges. Such analysis has shown that rotational velocities are, on average, higher for bulges than for comparable elliptical galaxies (Davies & Illingworth 1983, Kormendy & Illingworth 1982). Figure 1 shows that in bulges 
is close to unity, implying that these systems are flattened by rotation.
Confirmation that bulges can be adequately described as rotationally-flattenened systems has come from more complete model fitting. After allowing for the gravitational influence of the disk component, Jarvis & Freeman (1985) have shown that a simple rotationally-flattened model can reproduce both the photometric properties of edge-on bulges and the kinematics derived from spectra at many locations away from their major axes.
Study of the kinematics of edge-on bulges using multiple observations away from their major axes has also revealed that systems with boxy isophotes rotate cylindrically: their mean streaming velocities do not decline with distance from their central planes (Kormendy & Illingworth 1982). Such bulges have been modeled as rotationally-flattened axisymmetric systems (Rowley 1988), but the properties of boxiness and cylindrical rotation can also be ascribed to a prolate bar-like structure .
