midline

Bend that arm to row the weight up beneath your shoulder, then extend your arm back, behind the midline of your trunk.
5 Moves to Engage and Strengthen Your Glutes and Triceps|jversteegh|January 9, 2022|Outside Online
Using your triceps and the muscles behind your shoulder near your armpit, pull back against the band, moving your whole arm straight behind you, past the midline of your trunk.
5 Moves to Engage and Strengthen Your Glutes and Triceps|jversteegh|January 9, 2022|Outside Online
The track is directed strongly towards the midline of this creature’s foot, indicating that the dinosaur’s steps rotate inwards, a feature that isn’t typically seen among predatory dinosaurs.
After 60 years, a mysterious Australian dinosaur just got downsized|Margo Milanowski|October 22, 2021|Popular-Science
She chokes up midline — which is the line Bioware went with in-game — and there’s a great reason for that.
Every ‘Mass Effect’ squadmate, ranked from a storytelling perspective|Jhaan Elker|June 4, 2021|Washington Post

Immediately behind the hump is a series of knuckles or crenulations along the midline.
Whales, Dolphins, and Porpoises of the Western North Atlantic|Stephen Leatherwood
The single blowhole is located well to the left of the midline and far forward on the head.
Whales, Dolphins, and Porpoises of the Western North Atlantic|Stephen Leatherwood
Third vertebral scute: Length of anterior margin, 33; greatest width, 42; length at midline, 40 (estimated).
A New Extinct Emydid Turtle from the Lower Pliocene of Oklahoma|Edwin C. Galbreath
The pectoro-abdominal suture is anteriorly convex at the sides and concave at the midline.
A New Extinct Emydid Turtle from the Lower Pliocene of Oklahoma|Edwin C. Galbreath
Nuchal: Width of anterior margin, 12 (estimated); greatest width, 37 (estimated); length at midline, 35 (estimated).
A New Extinct Emydid Turtle from the Lower Pliocene of Oklahoma|Edwin C. Galbreath

Medical definitions for midline

midline

[ mĭd′līn′ ]

A medial line, especially the medial line or plane of the body.