Texas Government Code - GOV'T § 74.049. Performance of Duties by Chief Justice

(1) on the death or resignation of the presiding judge and until a successor presiding judge is appointed;

(2) on notification to the chief justice by the presiding judge or other appropriate source that an absence, disabling illness, or other incapacity of the presiding judge prevents the judge from performing his official duties for a period of time and until the presiding judge is again able to perform the duties;  and

(3) in a particular matter in which the presiding judge disqualifies himself from performing the duties of presiding judge in that matter.