300 THE SALAMANDER 



the duct enters the cranium. The first has been called the recessus 

 partis neglecta by Harrison who first described it. It is a short wide 

 diverticulum which comes into intimate contact with the ventral wall 

 of the pars neglecta, the separating wall being exceedingly thin. The 

 second diverticulum is smaller and is the recessus partis hasilaris of 

 Harrison. It bears a similar relation to the pars basilaris. 



These three areas, at the pars neglecta, pars basilaris, and sacculus, 

 where the membrane separating the perilymph from the endolymph 

 is extremely thin, are spoken of by Harrison as 'tympanal areas', and 

 it is, he supposes, through these areas, and through them alone, that 

 the vibrations imparted to the perilymph by the operculum are trans- 

 mitted to the endolymph. By these vibrations the otolith crystals in 

 the sacculus and lagena are set in motion, and these in turn affect the 

 sensory 'hairs' on the surface of the cells covering the maculae acus- 

 ticae, and thus the auditory nerve is stimulated. The function of the 

 saccus endolymphaticus within the cranial cavity is presumably similar 

 to that of the foramen rotundum of the mammalian ear, namely to 

 act as a buffer for the vibrations of the perilymph. 



II. THE EYE 

 I. General. 



The eye of the Salamander is relatively large and stands up promin- 

 ently from the surface of the head. The bulhus oculi is nearly spherical, 

 and, in the larva, is protected by a scleral ring of cartilage which, 

 however, disappears at metamorphosis so as to leave no trace in the 

 adult. The lens is also nearly, but not quite, spherical. According 

 to Beer (1899) accommodation is not effected by a change in the 

 curvature of the lens but by an alteration in its position, since he 

 finds that it moves towards the iris on stimulation. This movement 

 is brought about by a ciliary muscle which constricts the back 

 chamber and so forces the lens out, while the iris is said to play a 

 small but unimportant part. 



Klingelhoffer (19 10- 11) shows that the refractive index of the 

 Amphibian eye in general is such that it is a little long-sighted in 

 water, and that the lens, being less truly spherical than that of the 

 fish, and possessing some slight capacity for accommodation, is truly 

 intermediate between an aquatic and an aerial structure. 



Johnson (1926) during the course of an ophthalmological investi- 

 gation of Amphibian and Reptilian eyes found that 'Salamandra 

 maculosa exhibits the simplest and apparently the most primitive 

 condition of the disc.^ It is quite round and very small, being only 

 ' The point of entry of the optic nerve, E.T.B.F. 



