SiG 
the wall of the vestibulum nasale, a layer of cavernosus 
tissue, consisting of a framework of connective tissue and smooth 
muscle fibres, and of a system of communicating sinuses which are 
enclosed by this framework. 
3. Hydrophis (Hardwickii?) exhibits a remarkable development of 
cavernous tissue in the wall of the nasal vestibule. 
4. In Tropidonotus natrix and Vipera berus there occurs only a 
small amount of cavernous tissue in the immediate neighborhood of 
the external nares, there is, however, a musculus subnasalis 
which arises from the anterior margin of the horizontal part of the 
septo-maxillare and inserts on the ventral part of the Plica nasalis. 
The musculus subnasalis is composed of smooth fibres. 
Concerning the relation of the sinuses of the cavernous tissue of 
the nasal vestibule to the blood vessels of the head the following may 
be said: In Lacerta these sinuses are fed directly by small arteries 
belonging to the system of the arteria dentalis superior, and are 
drained by the venae jugularis facialis and palatina. In Hydrophis 
the sinuses of the cavernous tissue are fed by the arteria dentalis 
superior and drained by the very large vena palatina. 
In the cavernous tissue of the nasal vestibule, we have, without 
question, an apparatus by means of which a predominance of blood- 
pressure in the sinuses over the tension of the muscle-fibres of the 
trabecula will produce a thickening of the cavernous layer and a con- 
sequent diminution or complete closing of the nasal passage, while an 
excess of muscular tension over the blood-pressure would produce the 
contrary effect. The exact mode of regulating the blood-pressure in 
the sinuses, as well as the precise function of the cavernous tissue 
in specific cases, must be left for treatment in the detailed report of 
this investigation. At any rate is the occurrence of smooth muscles 
and cavernous tissue in the nasal vestibule of Reptilia highly inter- 
esting. 
