THE MIDDLE EAR. 61 



several nuclei, each of which may again contain several distinct 

 nucleoli. Amongst the processes there are usually one larger 

 and from two to five smaller ones. The former, after running 

 a variable distance, usually joins with another similar body, or 

 gives off branches that unite with the processes of other cells, 

 and these lead to the formation of plexuses. The smaller 

 processes branch in a tree-like manner, and ultimately run out 

 into fine processes that under favourable circumstances may be 

 seen to join with nucleated cells. Both the body of the cell 

 and the cell processes, but especially the former, appear to be 

 finely striated and invested by a finely granular mass. Whilst 

 those cells provided with a single nucleus resemble in form the 

 ganglion cells of the spinal cord, those which contain several 

 nuclei are very similar to rayeloplaxes. If the latter make 

 the multiplication of nuclei highly probable, this will be 

 rendered certain where disk- shaped appear to be converted 

 into globular cell bodies by the multiplication of nuclei. 



Before we now leave the tympanic cavity, we may still add 

 a few words respecting the ossicula, their connection with one 

 another, and the muscles attached to them. The ossicula are 

 invested with mucous membrane and in adults with a very 

 thin periosteum. Externally they are composed of compact 

 and internally of cancellous tissue. The latter is traversed by 

 numerous bloodvessels, which, passing through the compact 

 layer, communicate with the vessels of the periosteum or of the 

 mucous membrane. In the head and cervix of the malleus, as 

 well as in the body of the incus, the cancellous tissue increases 

 at the expense of the cortical layer; whilst the converse occurs 

 in the long and short processes of the incus and in the maiiu- 

 brium of the malleus. The articulations of the ossicula agree 

 in their structure with other true joints, having capsular liga- 

 ments, whilst a layer of hyaline cartilage covers the articular 

 surfaces. 



The mode of attachment of the stapes to the fenestra ovalis 

 will be more minutely described when the soft parts of the 

 vestibule are under consideration. 



The muscles of the ossicula are transversely striated, and 

 their tendons, where they traverse the interior of the tympanic 

 cavity, are covered by the mucous membrane by which it is 



