The nervus terminalis (cranial nerve zero) was investigated in 22 routine microslide series of different bat genera, mainly Myotis myotis, from 14 mm crown-rump length (CRL) up to adulthood, including cell measurements. Additionally, sections of other juvenile and adult bats treated immunocytochemically for LHRH were used. The total number of terminalis cells within the cranial vault was counted using conventional cytological criteria.
At 14 mm CRL, Myotis embryos already show a relatively large number of cells (about 700 cells on each side). In slightly larger specimens, the terminalis cell number first increases but then decreases markedly. It reaches its peak in late fetal stages and eventually is reduced to a minimum after birth. Interestingly, the number of meningeal terminalis cells is not correlated with body size. In this respect, Myotis holds an intermediate level while cetaceans show the absolute maximum in terminalis cell number within mammals.
The nervus terminalis, which includes at least two or more neurone populations, may play a different role both in successive ontogenetic periods and in the adult stages of various mammalian groups. The potential functional implications of the terminalis system in ontogeny and physiology are discussed.