Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 536 COMPAEATIVE ANATOMY. from the lower divisions upwards. In Fishes there is an indication of it in the form of a diverticulum, generally a small one, of the sacculus. In the Selachii it contains a number of small otoliths; in the Teleostei one larger one (asteriscus). In the Amphibia this diverticulum of the sacculus is more independent, but it is still connected as before, and is still directed backwards. This portion, which carries the end of a branch of the auditory nerve, is still fu
Elements of Comparative Anatomy (1878) Elements of Comparative Anatomy elementsofcompar78gege Year: 1878 536 COMPAEATIVE ANATOMY. from the lower divisions upwards. In Fishes there is an indication of it in the form of a diverticulum, generally a small one, of the sacculus. In the Selachii it contains a number of small otoliths; in the Teleostei one larger one (asteriscus). In the Amphibia this diverticulum of the sacculus is more independent, but it is still connected as before, and is still directed backwards. This portion, which carries the end of a branch of the auditory nerve, is still further differentiated in the Reptilia and Aves, where the diverticulum, which forms it (Fig. 300, G D E c), is a short conical piece, which is directed downwards from the median wall of the labyrinth, and converges towards its fellow of the opposite side. Its end is somewhat bent, and it forms the ' lagena.' Among Mammals this stage of the organ is seen in the Monotremata only; in the rest this stage is not the permanent one, for the organ is converted into a spirally-coiled canal. At first it is only formed by a prolongation of the saccnlus, but special differentiations appear in it, and this cochlear canal, which is formed from the sacculus, is permanently connected with it by a narrower portion only (canalis reuniens. Fig. 302). The organ, which thus becomes more indepen- dent, is sur- ff _ rounded on two sides of its course by lymphatic ca- vities, which accompany it in its coils, and pass into one another at the apex of the cochlea. One cavity is connected with the os- seous vesti- bule, the other is shut off from it at its commence- ment, and is only con- nected with the cavity of the vestibule indirectly; that is by the communication at the apex of the cochlea. Three cavities, therefore, can be dis- tinguished in the Mammalian cochlea; but one only, the ductus cochlearis, is connected with the vestibular labyrinth. The other two form the scalse—the sc. vestibuli and sc.
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