CARTILAGINOUS SEGMENT OF THE EUSTACHIAN TUBE. 69 



It further appears from such transverse sections, that the 

 transition of the osseous into the cartilaginous tuba Eustachii 

 is very gradual. Cartilage cells appear in the dense fibrous 

 tissue at some distance from the bony tube, at first scat- 

 tered, but subsequently in larger numbers. The curved 

 hook-like portion of cartilage of the Eustachian tube in Man, 

 which is attached by means of the so-called fibro-cartilago 

 basilaris to the base of the skull, is of moderate thickness, and 

 consists of non-vascular cartilage, which, as Kolliker states, 

 belongs to the same series of structures as hyaline cartilage. 

 Its hyaline matrix, containing a few fibres, includes isolated 

 groups of rounded and oval cartilage cells, of various size. 

 The larger cells contain two or more nuclei, the smaller cells 

 only one. Near the surface the cells become gradually smaller, 

 and there is here a layer of nucleated connective tissue, which 

 represents a perichondrium. No well-defined line exists be- 

 tween the perichondrium and the proper substance of the 

 cartilage, but the one kind of tissue runs gradually into the 

 other. At a few points this vascular tissue dips more or less 

 deeply into the cartilage, so as to form little islands in trans- 

 verse section, which i-nclude, in the Ox, small acinous glands. 

 The fibrous layer is much more strongly developed at the 

 lateral truncated extremity of the cartilaginous hook than 

 elsewhere, which is partly caused by the attachment of the 

 tendon of the musculus dilatator tubse to it. 



In the Quadrumana, as well as in Cheiroptera, the cartilage 

 of the Eustachian tube is hyaline, and very similar to that of 

 Man, the fibrous substance, especially in Bats, being almost 

 suppressed, whilst the hyaline cartilage, containing moderately 

 large cells, greatly preponderates. The same remarks apply 

 to the Eustachian tube of Rodcntia, Pachydermata, and Rumi- 

 nants. In the latter the cartilage cells are small, and the whole 

 cartilage appears to be composed of several segments. 



Remarkable differences occur in the external form of the 

 cartilage in different animals. In Talpa Europsea, Arctomys 

 marmota, Canis vulgaris, Mustela martes, and Lutra, there is 

 a simple lamella or cylindrical rod of cartilage on the median 

 side of the tuba, which in Lutra contains a considerable amount 

 of calcareous deposit. In the Dog, Marten, and Otter, the 



