At the beginning of Luoyang Grottoes, why is the' shore' in Tiananma's dragon missing a cross?

Driving a Tianan horse, the dragon is among the strange people. This was written by Chen Tuan in Song Dynasty, which means to be a master. It can be seen that his mind is very high. But there are two typos in just ten words, one is that the shore is less than one horizontal, and the other is that the shore is less than one horizontal. The tour guide said that this was because Chen Tuan had never met a talented person in his life, and he deeply felt that life was full of regrets, which was reflected in calligraphy.