Reply #33: The following is perhaps a more detailed explanation...

[Make7]

... concerning how the exterior panels were connected to each other (emphasis added):

The exterior walls of WTC 1 and WTC 2, comprised of steel columns and spandrel plates, were designed to resist the lateral forces and a portion of the gravity forces. Above the 7th floor, the columns were welded steel plate box columns, spaced 3 ft 4 in. on center. The columns and spandrels were shop-assembled and welded into 36 ft high by 10 ft wide panels, which consisted of three columns and three spandrels as shown in Fig. 5–1 (WSHJ 1967a). These panels were erected on site by bolting the base plate of an upper column to a cap plate of a lower column. Such splices were staggered so that only one-third of the panels were spliced at each story level, except at the base of the building and at the mechanical floors where all of the panels were spliced at the same level.

http://wtc.nist.gov/NISTNCSTAR1-1A.pdf   (pdf page 130)

Now to determine what is meant by "the base of the building" in the paragraph above, I will refer you to this drawing found on pdf page 131 of the same document:



Obviously the connection of the normal exterior panels would start on top of the exterior tree panels, which may explain why we see horizontal as well as up/down breaks in this photo.

- Make7