Adventure Comics # 73 Cover (April 1942). The first image is a restored scan from a reprint of the story. Below that is a scan of an original copy of the published book.
See Jack already experimenting with exaggerated perspective as the main character’s hand reaches right off the page. Also notice the anatomy of the right arm — it’s more expressionistic than anatomically correct. Or maybe Kirby and Simon simply learning their craft. See also Jack never seems to have a specific light source, which adds a unique dynamism to the piece.
Looking at Jack’s 100 issue run on a book like Fantastic Four, one has to wonder how a character like Manhunter would have evolved if Jack had worked on that property for an extended period of time.