Final answer:
The correct word to fill in the blank for the anatomy course consisting of 23 lectures is 'series'. It accurately depicts a succession of lectures that are part of the educational curriculum.
Step-by-step explanation:
The anatomy course consists of a series of 23 lectures. In this context, the term 'series' is the most appropriate choice because it refers to a number of things, events, or lectures that come one after another in succession.
When we talk about lectures in an academic course, they typically occur in a sequential order, which is what 'series' implies. Other options such as pattern, ratio, array, or cluster do not aptly describe a succession of lectures that form part of an educational curriculum.
A pattern may suggest repetition, but not necessarily in a sequential order, while a ratio is more related to quantitative relationships between numbers. An array could suggest an orderly arrangement, but not necessarily a sequence, and a cluster denotes a group without implying a particular order.