The gemara on 53a brings a machlokes between rebbi and r. elazar b'rabi shimon whether the blood of the korban chatas which required "k'ranos" had to be placed on the 1x1 amah horns that protruded up on the 4 corners of the mizbeiach (r. elazar b'rabi shimon) or if the 4 amos from the top of the horn down had the status of the "horn" and was available for the placing of the blood of the korban chatas. The gemara says that according to rebbi there was a dispute when the blood was placed beneath the horns within the top 4 amos of the miz'beiach, whether it had to be placed on the sharpness of the corner. The issue seems to be dependent on the definition of the term "keren". Certainly it refers to the horn, but can also mean the corner. When the blood is placed on the actual horn it doesn't need to be on the corner, but when it is placed beneath the actual horn, it is a machlokes whether we require it to be placed on the sharpness of the corner (see rashi d.h. u'mar savar, who seems to support this explanation).
In the gemara 54b rav kahana explains that they would make hollow areas within the horns by placing small sticks in that they would pull out when the cement began to dry. Rashi explains that the purpose of these hollow areas was to contain the blood that was sprinkled on it. Tosafos asks on rashi that the blood wasn't placed on top of the horn, rather on the sharpness of the corner so it doesn't seem that the holes were there to absorb the blood? The ya'avetz says that he doesn't understand Tosafos. The gemara on 53a established that all agree the blood can be placed on the horns, in which case it doesn't need to be on the sharpness of the corner. Therefore, rashi is correct that the blood can be placed on the top of the horn and the holes were necessary to help it become absorbed. Perhaps Tosafos understood that although the blood doesn't need to be placed on the sharpness of the corner when it is actually placed on the horn, it would still be ideal to place the blood on the sharpness of the actual horn because that would fulfill both definition of the term "keren" - horn and corner.