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index 0e7e6d0fb..90b67c405 100644
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diff --git a/scrapy/trunk/docs/topics/_images/scrapy_architecture.png b/scrapy/trunk/docs/topics/_images/scrapy_architecture.png
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diff --git a/scrapy/trunk/docs/topics/architecture.rst b/scrapy/trunk/docs/topics/architecture.rst
index e61c72ef6..9fb9c0a02 100644
--- a/scrapy/trunk/docs/topics/architecture.rst
+++ b/scrapy/trunk/docs/topics/architecture.rst
@@ -18,7 +18,7 @@ also described below.
 
 .. image:: _images/scrapy_architecture.png
    :width: 700
-   :height: 468
+   :height: 494
    :alt: Scrapy architecture
 
 Components
@@ -77,6 +77,14 @@ requests). They provide a convenient mechanism for extending Scrapy
 functionality by plugging custom code. For more information see
 :ref:`topics-spider-middleware`.
 
+Scheduler middlewares
+---------------------
+
+Spider middlewares are specific hooks that sit between the Engine and the
+Scheduler and process requests when they pass from the Engine to the Scheduler
+and vice-versa. They provide a convenient mechanism for extending Scrapy
+functionality by plugging custom code.
+
 Data flow
 =========