THE FROG 73 



has demonstrated particular sensations for particular nerve endings in 

 the arm of man, so it may be supposed that these different end-organs 

 in the skin may have similar definite functions. 



THE SKELETON 



The frog is possessed of an endoskeleton as is man. The bones and 

 cartilages constituting this endoskeleton furnish a support, holding in 

 position all the muscles and organs of the body. 



For convenience's sake the skeleton is divided into two parts, the 

 axial portion (Fig. 20), comprising skull and vertebral column, and the 

 appendicular portion (Figs. 21, 22), consisting of the pectoral or shoul- 

 der, and pelvic or hip girdles, together with the bones of the limbs which 

 these girdles support. 



The frog's skeleton possesses about ninety articulated bones (united 

 at the joints). The skull has the various bones comprising it so firmly 

 fused that they appear as a single bone. Even the seemingly single 

 bone of the fore arm will be found to consist of two bones which have 

 also fused together. 



THE AXIAL SKELETON 



This is divided into the skull [cranium ( ) and 



visceral skeleton ( )], and vertebral column. The 



two divisions of the skull mentioned above are made up of the brain case 

 together with the auditory ( ) and olfactory cap- 



sules ( ) which constitute the cranium. The jaws 



and hyoid arch ( ) together, form the visceral skel- 



eton. 



The inside of the cranium where the brain is placed is known as 

 the cranial cavity. The skull itself is composed of thirty-two bones and 

 cartilages fused together so as to appear almost a solid structure. The 

 cranial bones form the roof, walls, and floor of the cranial cavity. 



The floor is composed of the basioccipital ( ) 



and the parasphenoid ( ). 



The walls consist of the parietals ( ), the otic 



bones ( ), and the exoccipital ( ). 



The roof is made up of the supraoccipital ( ) 



and the frontals. 



The facial bones, forming the face, consist of nasals ( ), 



the premaxillas ( ), and the maxillas ( ) 



above, and vomers ( ) below. The premaxillas and 



the maxillas, however, are a part of the visceral skeleton comprising, to- 

 gether with a pair of quadrangulars, the upper jaws. 



H and I. Vertebrae of a frog. H, fourth vertebra, seen from in front ; I, sixth 

 and seventh vertebrae from the right, az., Prezygapophysis ; cen., centrum ; n.a., 

 neural arch ; n.c., vertebral foramen ; n.s., neural spine ; r>z., postzygapophysis ; r.c., 

 cartilage at end of transverse process ; tr., transverse process. 



(A, B, C and D from Bourne, after Ecker. E, F, G, H and I, after Borradaile.) 



