Mesosternum(Anat) The middle portion, or body, of the sternum.
Mesosternum(Zoöl) The ventral piece of the middle segment of the thorax in insects.
Century Dictionary and Cyclopedia
nmesosternumIn anatomy, the piece or pieces of a breast-bone which has several segments lying between the presternum and the xiphisternum: said chiefly of the segmented sternum of mammals. In man it is the gladiolus or body of the sternum proper, as distinguished from the manubrium and the xiphoid cartilage.
nmesosternumIn entomology, the ventral or sternal sclerite of the mesothorax; the under side of the mesothorax, opposite the mesonotum.
Webster's Revised Unabridged Dictionary
Meso-, + sternum,
Mesosternum: the underside or breast of the meta-thorax.
"Explanation of Terms Used in Entomology" by John. B. Smith
II, Middle leg and mesosternum.
"Encyclopaedia Britannica, 11th Edition, Volume 13, Slice 4" by Various