12 University of California Publications in Zoology (Vou. 9 
The elongation of the symphysial cartilage into a rod-lke 
structure is found in other iguanids (Dipsosaurus dorsalis, 
Sceloporus occidentalis) but is developed to a less degree. The 
tendeney to ossify appears to be peculiar to the genera Phry- 
nosoma and Anota. 
Limbs: The limbs are short but typically lacertiian. A 
pisiforme, ulnare, intermedium, radiale, centrale, and five car- 
palia compose the carpus, and five metacarpalia, the metacarpus. 
The tarsalia are partly united with the metatarsalia. A well- 
developed claw tips the digits. 
INTEGUMENT 
The integument of the horned lizards is much lke that of 
other lizards except for a modification of the epidermis on the 
horns and the wide variation in size and shape of the dorsal 
seales. 
On the horns and larger spinous scales the epidermis is 
modified into a cartilaginous cap. This cap is shed with the skin 
and is regenerated by the laver of epidermis which remains. 
The rest of the epidermis is developed into horny plates or 
seales. The layer is continuous, the scales being formed by a 
thickening of the horny layer. The dorsal seales in this genus 
vary greatly in size and shape. Those of the back may be small 
and granular or large, keeled and tuberculated. Ventrally the 
seales are uniform in size and show a pavement-lke arrangement. 
The plates of the head are usually small and regular im size but 
show variation in each species. Enlarged scales are found on the 
mandibles and periphery. 
The horny epidermis is cast off periodically. This exuviation 
as shown by Bruner (1907), is caused by ‘‘a new growth of the 
stratum corneum beneath the old layer and a mechanical push- 
ing off, of the old stratum which has been eut off from its supply 
of moisture and nourishment.’’ This last part of the process is 
greatly aided by the growth of small prickles on the surface of 
the new layer. There is also a possibility that the formation of 
new capillaries may aid the process (Bruner, 1907). The molt- 
ing process often causes the lizard a certain amount of incon- 
