MUSTELUS L.EYIS. l49 



one lying near the roof of the orbit, one near its fJooi-, and 

 the other intermediate between the two. Schwalbe (57, p. 

 183) says that the ophthalmicus superficialis and ophthal- 

 micus profundus issued by a single foramen in the adult 

 specimen of Mustelus lasvis that he examined, the tri- 

 gemi no-facial nerves thus issuing* from the cranial cavity 

 by two instead of by thi-ee foramina. Tiesing (62), on the 

 contrary, shows, in the adult, three separate foramina exactly 

 as I find them in embryos. 



The dorsal one of the three trigeraino-facial foramina of 

 my embryos is the most anterior one of the three, and it 

 transmits the so-called ramus ophthalmicus superficialis, this 

 nerve containing a large component derived from the tuber- 

 culum acusticum, another large component derived from the 

 lobus trigemini, and a third and suialler one derived from the 

 so-called anterior or first root of the nervus trigemini. The 

 first two of these three components together form what is 

 now usually described as the ramus ophthalmicus superficialis 

 facialis, the third one being the ramus ophthalmicus super- 

 ficialis trigemini. The latter nerve is certainly largely com- 

 posed of general cutaneous fibres, though it may perhaps also 

 contain a certain number of communis fibres, for although 

 Haller says (p. 437) that in Scyllium the sensory part of 

 Trigemini I is formed entirely of fibres derived from the 

 ascending trigeminus tract, this tract is said to have pre 

 viously received a bundle of fibres coming from the lobus 

 vagi (p. 431). If, then, the anipullas of selachians represent 

 the terminal buds of Amia and teleosts, these fibres from 

 the lobus vagi must be so-called visceral-sensory communis 

 fibres, which have naturally not suffered the modification 

 that I assume that the terminal bud fibres are undergoing. 



The middle foramen is the next anterior one of the three, 

 and it transmits the ramus ophthalmicus profundus, derived 

 from a ventro-lateral and somewhat separate and independent 

 part of the intra-cranial trigeminus ganglion. 



The third trigemino-facial foramen is much the larger one 

 of the three. It lies venti'al and posterior to the other two, 



