Source description:
Out of the late Spencerian and P. D. & S. styles there has since been developed, from approximately about 1880, the modern commercial hand (Figs. 87, 88) , which has certain distinctive characteristics. This style of writing was perfected and popularized through the excellent work of the American commercial schools that for years have given special emphasis to rapid business writing. An essential element of this writing has been a free movement, in which the arm is brought into use in the writing process, and the forms adopted have been those best suited to easy, rapid writing. (Osborn 1910, page 181)

Observe in particular with the minuscules (lower case letters):

• plain cursive forms without shading or flourishing
• attention to clear and regular inter-letter spacing
• condensed ascenders and descenders
• some shortened upward entry strokes starting above baseline
• alternate forms such as 'p', 'r', and 'k'
  

Also some alternate terminal forms, used at the end of words, either for economy or aesthetics:

• non descending letters 'd' and 't', compare 't's in Writing and must
• descending letters 'g', 'j' and 'y', compare 'g's in Writing and legible

(see also Spencer Brothers' Abbreviated Hand plate 12, and Abbreviation of Small Letters page 20 in New Spencerian Compendium of Penmanship published in 1879)