At the center of NGC 4638, there is a small bulge. There is also an edge-on disk and a diffuse, boxy halo. The shallow surface brightness gradient of the halo is characteristic of a large spheroidal galaxy. This means that NGC 4638 has properties of both S0 and Sph galaxies.[8]
^Binggeli, B.; Sandage, A.; Tammann, G. A. (1985-09-01). "Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area". The Astronomical Journal. 90: 1681–1759. Bibcode:1985AJ.....90.1681B. doi:10.1086/113874. ISSN0004-6256.