on the ventral face of the outer condyle, which passes between the tibia and the fibula, as in birds.
11. The tibia is shorter than the femur. Its proximal end is produced anteriorly into a strong crest, which is bent outwardly, or towards the fibular side.
12. The astragalus is like that of a bird; and the digits of the pes are terminated by strong and curved ungual phalanges.
The Dinosauria about which we have sufficient information appear to me to fall into three natural groups—i. the Megalosauridæ, ii. the Scelidosauridæ, and iii. the Iguanodontidæ.
i. The Megalosauridæ.
1. The maxillary teeth are sharp-pointed, and the crown has a longitudinal serrated ridge, either on the middle of its posterior face only, or on the middle of its anterior face as well. The serrations of the ridge are directed at right angles to the long axis of the tooth. The teeth do not become worn by mastication.
2. The anterior prolongation of the ilium is nearly as large as, or larger than, the posterior.
3. The rami of the mandible are deep and thick and meet by rounded ends in the symphysis.
4. The proximal end of the femur is flattened, curved, and twisted in such a manner that its plane is oblique to that of a flat surface on which the condyles rest. In other words, it is more or less crocodilian.
5. There is no dermal armour.
Teratosaurus, Palæosaurus, Megalosaurus, Poikilopleuron, Lælaps, and probably Euskelosaurus belong to this group.
ii. The Scelidosauridæ.
1. The maxillary and mandibular teeth have sharp-edged triangular crowns, with serrated margins, the serrations being oblique to, or parallel with, the long axis of the tooth. The teeth are not worn down by mastication.
2. The anterior prolongation of the ilium is more slender than the posterior.
3. The rami of the mandible are slender, and taper to their symphysis.
4. The proximal end of the femur has a subglobular articular head, borne by a neck which is set nearly at right angles to the axis of the shaft, while its direction is nearly parallel with a flat surface on which the condyles rest.
5. The integument is (usually) provided with a dermal armour in the form of bony scales or spines.
Thecodontosaurus, Hylæosaurus, Polacanthus(?), and Acanthopholis belong to this division.
iii. The Iguanodontidæ.
1. The maxillary and mandibular teeth have obtuse subtriaugular crowns; the surface of the enamel being ridged on one or both sides. The crowns of the teeth are worn down flat by mastication.
