148 EDWARD PHKLP8 ALMS, .TUN. 



the brain — the lobus trigeniini; and the tuberculum acusticum. 

 The assertion that the lobus trigemini is a part of the 

 tuberculum acusticum^ somewhat differentiated as a separate 

 lobus, does not seem sufficient in itself to account for this 

 ori,<>;in in Selachians, and also in Acipenser (39), of the 

 so-called lateral fibres from two distinct centi'es, while in 

 ganoids and teleosts they arise from a single centre, the 

 tuberculum acusticum (40). While I have wholly failed in 

 my attempt to trace in Mustelus the fibres from the 

 lateral canal organs to one of these two centres, and those 

 from the anipullary organs to the other, it is evidently a 

 legitimate supposition that such may perhaps be their 

 central origin, and this has already been suggested by 

 Strong (60, p. 194). If it be admitted, the natural con- 

 clusion must be, as Strong has said, that the anipullary 

 organs represent the terminal buds of Amia and other fishes, 

 and not organs similar to the pit organs found on the head of 

 Amia. That tiie ampullee may be derived from, or be directly 

 related to, certain of the so-called pit-organs of current 

 descriptions of teleosts is, however, quite probable, and will 

 be again referred to. 



The facial root of the trigemino-facial complex of Mustelus 

 arises in my 55 mm. embryo by two rootlets, one of which 

 has its central origin in the lobus vagi, while the other 

 contains motor fibres, Mustelus thus apparently full}- agreeing 

 with Scyllium. On this facial root there is no important 

 intra-cranial ganglion, though ganglion cells begin on its 

 dorsal surface just before it leaves the skull. It issues 

 through the postero-ventral part of the large trigemino-facial 

 foramen, and a large extra-cranial ganglion immediately 

 forms on it, this ganglion being somewhat separate from the 

 extra-cranial ganglion on the truncus maxillo-mandibularis, 

 and lying postero-ventral to it. 



The trigemino-facial nerves of my embryos of Mustelus 

 thus issue from- the skull by the three well-known trunks or 

 stems, and each stem has its own special foramen. All three 

 of these foramina pierce the cranial wall in the oi'bital region, 



