get() return nothing

Hello, there,
I wrote a loop to check the dimension of all the .txt dataframes:> ls()
 [1] "actualpca.table" "b4galnt2"        "b4galnt2.txt"    "data"
 [5] "galnt4"          "galnt4.txt"      "galnt5"          "galnt5.txt"
 [9] "galnt6"          "galnt6.txt"      "glyco"           "glyco.txt"
[13] "i"               "mtscaled"        "newsig.table"    "nicepca"
[17] "pca"             "sig.txt"         "st3gal3"         "st3gal3.txt"
[21] "st3gal5"         "st3gal5.txt"     "st6gal1"         "st6gal1.txt"

for(i in ls(pattern="txt")){dim(get(i))}

If I check individual ones, they are ok:

dim(get("galnt4.txt"))

[1] 8 3

could anyone help me to figure out why it did not work with a loop?
Thanks a lot!