Comparing the classical descriptions with what is taught under the same names today is usually an exercise in discontinuity. Names have moved between shapes, shapes have been rebuilt around different joints, and a large part of the modern repertoire, the standing sequences above all, has no counterpart in the medieval manuals at all. Mark Singleton's Yoga Body traces how the practice that spread worldwide in the twentieth century was assembled from the hatha inheritance together with Indian physical culture and European gymnastic systems, which is why the correspondence between text and studio is so often loose.
Bhujangasana is the exception that makes the pattern visible. The shape the Gheranda Samhita describes, prone from the navel down, palms planted, head and chest raised, is recognisably the shape taught under that name now. Of the thirty two postures in the later manual it is the one that has travelled furthest with the least alteration.
That continuity does not extend to the framing. The text presents the posture as heating the body and rousing the serpent goddess; modern instruction generally presents it as work for the spine and the front of the body. The same arrangement of limbs is doing an entirely different job in the two accounts, which is a reminder that a posture is not only a shape. The atlas records the classical claims as the classical texts make them and does not restate them as effects.