Premaxillary teeth in deep sockets. The teeth of other synapsids are implanted in shallow sockets. In other synapsids, the septomaxilla is restricted to the external naris, except in most therapsids, where it has a large facial exposure. Postcaniniform teeth robust, chisel- shaped. The shape of marginal teeth is quite variable in early synapsids, but their morphology in H. garnettensis is unique.
Teeth present on the palatal ramus of the premaxilla.
In other synapsids, this bone only bears marginal teeth. A contact between the postorbital and the supratemporal. In other synapsids, the posterior end of the dentary is near the dorsal edge of the jaw. Braincase firmly sutured to back of dermal skull roof. The braincase of most other synapsids is attached fairly loosely to the posterior edge of the cheek and skull table.