A 52-year-old man from Delhi presents with progressive dysphagia and substernal chest pain for 3 months. Upper endoscopy reveals a 4 cm irregular ulcerated lesion in the mid-esophagus. Biopsy is taken and sent for histopathology. Under the microscope, the pathologist observes stratified squamous epithelium with invasion of malignant cells into the lamina propria, with areas of keratinization. No glandular differentiation is noted. Which of the following histological features would be MOST characteristic of the normal esophageal mucosa that is being invaded by this tumor?