THE SKULL. 23 



A. THE CRANIUM. 



The cranium of the frog is a prismatic tube, wide behind, narrow 

 in front, and formed in great part of cartilage (Figs. 1 5 and 17). Our 

 indigenous species are characteristically distinguished from one 

 another by peculiarities in the form of the cranium. In JLacultafa 

 it is long and narrow, in R . temporaria short and wide. The superior 

 surface in the former is markedly concave, while in the latter it is 

 flat, and in R. oxyrJiinv.s arched. These differences are readilv 

 recognised in the living animal. 



The Bones of the Cranium. 



1. Tke exoccipital bones, ossa oedpiiaKe lafrral.la, Cuvier 

 (Figs. 10, u, 12, 14- 



Cuvier, /. c., p. 387, PI. XXIV. bb. Duges, /. c.. n. 14. Parker and Bet- 

 tany, /. c., p. 166, Woccipitals. 



These paired bones form the hinder part of the cranium ; they 

 bound the foramen magnum, and articulate with the vertebral column. 



Thev are imbedded in the cartila- 







ginous matrix of the skull, and are 

 separated above by an unossified 

 part of this matrix (occipitalc 



superiu.*, Duges), which represents 

 the tabular portion of human 

 auatomv: below thev arc separated 



.* * . . A . twice natural size. 



by a similar part (<>cc/jj/fa/>- hiti- a stapes. 

 lore, Duges) which represents the J, ^S^SIj!' 



bodv of the Occipital bone. They Condyles of exoccipitafe. 



ji. _ i k Stvlo-hyoid. 



therefore properly represent only E i.xv 

 the condvlar portions (paries con- p . ^" 



p Process to which the jaw is attached. 



dyloideae) of the human occipital t squamosaL 

 bone. Each \ cartilaginous articular head, for articulation 



with the first vertebra : these converge below, and sunound the 

 lower half of the circumference of \}\e foramen in annum. This latter 

 has, in E. esi.-n.friifa, a transversely oval outline ; in E. few/joraria, a 

 somewhat heart-shaped outline, with the apex directed upwards : 

 in accordance with this the whole bone is wider than high in the 

 first species ; and in the latter it is higher than it is wide. From 

 the upper and outer border of the foramen wag n it/it on each side 



