The Boston’s ears are small, carried erect and either natural or cropped to conform to the shape of the head. The Frenchie’s ear, known as the “bat ear,” is naturally erect, rounded at the top and broad at the base, carried with the orifice toward the front and set not too close together. The ear is moderate in size, neither too large nor too small, but in proportion to the size of the head. The Frenchie’s ears are ideally set high on the head at approximately 11 and 1 o’clock. The top skull of both breeds is flat between the ears. The Boston has no ear DQs; the Frenchie has a DQ for any ear other than a bat ear.
The Frenchie’s eyes are round in form and of moderate size, neither bulging nor sunken. They are preferably dark in color and set low down in the skull as far from the ears as possible. In lighter-colored dogs, a lighter eye is acceptable. While more pleasing, pigmented eye rims are not required by the standard. In contrast, the Boston Terrier has large, round and dark eyes set wide apart, with blue eyes or any trace of blue in the eye disqualifying.
Moving to the nose, which in the Boston is black and wide with a well defined line between the nostrils. A Dudley nose disqualifies. The Frenchie’s nose is black and extremely short with broad nostrils and a well defined line between them. A nose other than black is a Frenchie disqualification except in the case of lighter-colored dogs, where a lighter-colored nose is acceptable but not desirable. “Lighter-colored dogs” refers to creams and self-masked fawns whose nose color can typically range from black to self-colored. However, there must still be some pigment and without pink spots, as that would be a multicolored nose, which would disqualify. Black-masked fawns (and BMF pieds) are not lighter-colored and must have a black nose. Brindle pieds are also not lighter-colored, as the pied gene is a pattern gene, and they are actually patterned, brindle dogs that must have a black nose. Cream and white pieds or “honey pieds” would be considered lighter-colored because their base color is cream or self-masked fawn.
The Boston’s muzzle is short, square, wide, deep and in proportion to the skull. It is free from wrinkles, shorter in length than in width or depth, and not exceeding in length approximately one-third of the length of the skull. The muzzle from stop to end of the nose is parallel to the top of the skull. The Frenchie’s muzzle is typically shorter in length than the Boston’s, and is broad, deep and well laid back, with well developed cheek muscles. Its extremely short nose results in an extremely short muzzle. Both breeds have broad, square underjaws which in the Frenchie is deep, undershot and well turned up. In the Boston, the underjaw is level or sufficiently undershot to square the muzzle, without the upturn called for in the Frenchie. In both breeds, the flews should cover the teeth when the mouth is shut.

While the Boston’s topline is level, the Frenchie’s roached topline has a slight fall close behind the shoulders and rises to the loin. Although not detailed in the standard, the topline description in the Bulldog standard is applicable:

“Topline — There should be a slight fall in the back, close behind the shoulders (its lowest part), whence the spine should rise to the loins (the top of which should be higher than the top of the shoulders), thence curving again more suddenly to the tail, forming an arch (a very distinctive feature of the breed), termed ‘roach back.’” photo by © Daniel Kis-Szabo
It is unfortunate that we often see Frenchies with level Boston toplines and Bostons with roached Frenchie toplines in the ring. A correct topline is probably one of the most difficult characteristics to breed, which is why we find such variety. If either breed has a correct topline, it will likely have a correct low tail set. The Frenchie’s tail, like the Boston’s, is either straight or screwed, and is set low and carried low. The Boston tail must not be carried above the horizontal, and neither should the Frenchie’s. A docked tail is a disqualification in both breeds, as it would be considered an alteration in the Frenchie. Correct set and carriage in both breeds are more important than actual tail length, and in the Frenchie the tail may be so short as to almost not be apparent; however, there will still be a tail. In almost 40 years of owning and breeding Frenchies, I have never seen a Frenchie with an ingrown tail.
The Frenchie’s forelegs are short, stout, straight, muscular and set wide apart. “Short” must again be taken in its historical context, when the Frenchie was a much rangier, longer-legged dog. Although Frenchies are not a square breed, they should also not be reminiscent of caterpillars, with long bodies and overly short legs. Such dogs are often achondroplastic dwarfs and must never be rewarded in the show ring. The Frenchie’s hindquarters are strong and muscular and slightly longer than the forelegs such as to elevate the loins above the withers.
The Boston’s forequarters are well laid back, with sloping shoulders, which allows for the Boston’s stylish movement. The forelegs are straight in bone and, unlike the Frenchie, are set only moderately wide apart, resulting in a narrower-appearing dog. Hindquarters have strong, well-muscled thighs, with good bend of stifle and short hocks; straight stifles are a fault. The Frenchie standard does not mention rear angulation, but being a moderate breed, they should neither be over-angulated nor straight behind. Moderate angulation allows the free, vigorous and unrestrained movement called for in the standard.