230 T'ransactions.—Zoology. 
skull, with its two bars and additional bones, the pharyngeal eavity is 
enormously enlarged. When the-tuatara inspires it greatly depresses the 
hyoid and trachea, thereby still more enlarging the pharyngeal cavity. By 
this means the tuatara inhales a large quantity of air, filling the lungs, 
mouth, trachea, and the large pharyngeal cavity. This peculiar mode of - 
respiring by depressing the hyoid bone (which with its cornea is very 
large) enables the tuatara to inhale sufficient air to allow it to remain under 
water for hours without coming to the surface to breathe. The quantity of 
air in the lungs, trachea, mouth, and distended pharynx amounts to several 
cubic inches, which is sufficient to sustain life for some time in a small and 
cold-blooded reptile. 
Tuataras swim freely—sometimes with only the nostrils above water, at 
others swimming as freely and well under it. As tuataras are found usually 
on isles, or on the banks of rivers, it may be that they find part of their 
food in the water. The Ichthyosaurus and Plesiosaurus marine reptilia had 
abdominal ribs, and the former amphiccelian vertebrz like the Sphenodon. 
Dissection of Female Tuataras. 
Total length, 16 inches, of which 83 inches were tail. Dorsal spines 
beginning at the occiput stretch along the back to the end of the tail; 
between the scapule five or six are wanting, and about three over the 
sacrum. Those on the neck and trunk are flattened laterally, blade-like, 
and acuminated ; they are quite soft, and many are not erect. The caudal 
spines are attached one to each section of the verticellated tail. About the 
middle of the tail, instead of being flattened laterally they are prismoidal, 
being much wider at the base and not so sharp. As the tail sections 
dwindle so also do the spines till they can scarcely be said to exist. This 
tuatara has ten cervical spines, then an interval between the shoulders, 
then fifteen dorsal, an interval over the sacrum, and forty-one caudal spines. 
In Lophocalotes interruptus the spines, as in Sphenodon, reach from the head 
to end of tail, and are also interrupted between the scapula and over the 
sacrum. So also in Tiaris tuberculata; in this lizard there is on each side a 
row of secondary spines. In Sphenodon, as in certain other lizards where 
the spines are absent between the scapula, their place is occupied by a large 
black patch of skin; some spines are also black. The skin of Sphenodon is 
marked by several ridges which reach from head to tail, running parallel 
with the dorsal crest. One ridge extends along the trunk from the fore to 
the hind limbs ; it is due to the free projecting ends of the abdominal ribs. 
Two ridges beginning at the end of the rounded snout run backwards 
above the nasal openings and the eyes, giving a triangular look and a flat 
appearance to the form of the head. In many places the epithelial cells are 
accumulated, forming small spines which irregularly crown some of these 
skin ridges. ; 
