this point是指the first six generations吗?

The Tracheobronchial Tree

An accurate and complete model of the branching pattern of the human bronchial tree remains elusive, although several different models have been described. The most useful and widely accepted approach remains that of Weibel,2 who numbered successive generations of air passages from the trachea (generation 0) down to alveolar sacs (generation 23).This ‘regular dichotomy’ model assumes that each bronchus regularly divides into two approximately equal size daughter bronchi. As a rough approximation it may therefore be assumed that the number of passages in each generation is double that in the previous generation, and the number of air passages in each generation is approximately indicated by the number 2 raised to the power of the generation number. This formula indicates one trachea, two main bronchi, four lobar bronchi, 16 segmental bronchi and so on. However, this mathematical relationship is unlikely to be true in practice, where bronchus length is variable, pairs of daughter bronchi are often unequal in size, and trifurcations may occur.

气管支气管树

虽已经描述过几种不同的人类支气管树分支模型，但精确且完整的模型仍不明确。Weibel模型2仍是最有用最广泛接受的模型，Weibel模型把连续的各级气道从气管（0 级）到肺泡囊（23 级）进行编号。这种“规律的二分法”模型假设每个支气管规律地分成两个大小大致相等的子支气管。因此，可粗略的假设每一级的气道数是上一级的两倍，并且每一级的气道数可以近似地用本级气道级数的2次方表示。该公显示：1个气管、2个主支气管、4个叶支气管、16个段支气管，以此类推。然而，这种数学关系在实际中不太可能成立，因为支气管的长度不定，成对的子支气管通常大小不等，并且可能出现三个分叉。

Work using computed tomography to reconstruct, in three dimensions, the branching pattern of the airways has shown that a regular dichotomy system does occur for at least the first six generations.3Beyond this point, the same study demonstrated trifurcation of some bronchi and airways that terminated at generation 8. T able 1.1 traces the characteristics of progressive generations of airways in the respiratory tract.

使用计算机断层扫描进行气道分支的三维重建显示，至少在前六级气道中确实存在“规律的二分法”体系3。超过前六级，同一研究表明某些支气管和气道的三分叉在第8级终止。表1.1 描述了呼吸道中各级气道的特征。

各位老师，this point是指the first six generations吗?如果是的话，也就是1-6级是“规律的二分法”，7-8级可以出现“三分法”，但也只有7-8级可以出现“三分法”？谢谢